UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  ☒                             Filed by a Party other than the Registrant  ☐

Check the appropriate box:

Andeavor Logistics LP

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

Payment of Filing Fee (check the appropriate box):

Dear ANDX Common and Series A Preferred Unitholders:

Pursuant to an Agreement and Plan of Merger, dated as of May 7, 2019 (the “Merger Agreement”), the general partner of Andeavor Logistics LP (“ANDX”), which is Tesoro Logistics GP, LLC (“ANDX GP”), and the general partner of MPLX LP (“MPLX”), which is MPLX GP LLC (“MPLX GP”), on behalf of each of ANDX and MPLX, have approved the combination of the businesses of ANDX and MPLX. Pursuant to the Merger Agreement, MPLX MAX LLC, a direct, wholly owned subsidiary of MPLX (“Merger Sub”), will merge with and into ANDX, with ANDX being the surviving entity and becoming a wholly owned subsidiary of MPLX (the “Merger”). Both ANDX GP and MPLX GP are indirect, wholly owned subsidiaries of Marathon Petroleum Corporation (“MPC”), and as a result, MPC controls both ANDX and MPLX.

As a result of the Merger, (a) each common unit representing a limited partner interest in ANDX (each, an “ANDX Common Unit” and, collectively, the “ANDX Common Units”), other than any ANDX Common Units held by ANDX GP and Western Refining Southwest, Inc. (“ANDX Refining Southwest”) (such ANDX Common Units, the “Public Unitholder Eligible Units”), issued and outstanding immediately prior to the effective time of the Merger will be converted into the right to receive 1.135 common units representing limited partner interests in MPLX (“MPLX Common Units”) (such exchange ratio, the “Public Unitholder Exchange Ratio”); (b) each ANDX Common Unit held by ANDX GP and ANDX Refining Southwest issued and outstanding immediately prior to the effective time of the Merger will be converted into the right to receive 1.0328 MPLX Common Units (such exchange ratio, the “Affiliated Unitholder Exchange Ratio”); (c) each 6.875% Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Unit, liquidation preference $1,000 per unit, representing a limited partner interest in ANDX (each, an “ANDX Series A Preferred Unit” and, collectively, the “ANDX Series A Preferred Units”) issued and outstanding immediately prior to the effective time of the Merger will be converted into the right to receive a Series B Preferred Unit representing a substantially equivalent limited partner interest in MPLX (each, an “MPLX Series B Preferred Unit” and, collectively, the “MPLX Series B Preferred Units”); (d) each TexNew Mex Unit, as such term is defined in the Third Amended and Restated Agreement of Limited Partnership of ANDX, as amended (the “ANDX Partnership Agreement”), issued and outstanding immediately prior to the effective time of the Merger will be converted into a new class of units of MPLX with substantially equivalent rights, powers, duties and obligations as the TexNew Mex Units; and (e) the interest in ANDX that confers upon the holder thereof only the rights and obligations specifically provided in the ANDX Partnership Agreement with respect to the “Special Limited Partner Interest” (the “ANDX Special Limited Partner Interest”) will be converted into a new limited partner interest in MPLX with substantially equivalent rights, powers, duties and obligations as the ANDX Special Limited Partner Interest.

Additionally, at the effective time of the Merger, each phantom unit issued under ANDX’s 2011 Long-Term Incentive Plan, as amended and restated, and the Western Refining Logistics, LP 2013 Long-Term Incentive Plan (each, an “ANDX Phantom Unit” and, collectively, the “ANDX Phantom Units”), whether vested or unvested, other than any ANDX Phantom Unit that is held by a non-employee director of ANDX GP (each, an “ANDX Director Phantom Unit” and, collectively, the “ANDX Director Phantom Units”), will automatically be converted into a phantom unit denominated in MPLX Common Units (the “Converted MPLX Phantom Units”). The number of ANDX Common Units subject to the ANDX Phantom Units immediately prior to the effective time of the Merger will be converted into a number of MPLX Common Units subject to the Converted MPLX Phantom Units based on the Public Unitholder Exchange Ratio (rounded down to the nearest whole number). ANDX Director Phantom Units will generally be converted into the right to receive a cash payment equal to the number of ANDX Common Units subject to such ANDX Director Phantom Unit multiplied by the product of the Public Unitholder Exchange Ratio and the average of the volume weighted average price per unit of MPLX Common Units on the New York Stock Exchange (the “NYSE”) on each of the ten consecutive trading days ending with the complete trading day immediately prior to the closing of the Merger.

ANDX Common Units currently trade on the NYSE under the symbol “ANDX,” and MPLX Common Units currently trade on the NYSE under the symbol “MPLX.”

The conflicts committee (the “ANDX Conflicts Committee”) of the board of directors of ANDX GP (the “ANDX Board”) unanimously determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are in, or not opposed to, the best interests of ANDX and its subsidiaries treated as a single consolidated entity and the holders of Public Unitholder Eligible Units, approved and declared advisable the Merger and the consummation of the transactions contemplated by the Merger Agreement (the foregoing constituting “Special Approval” under the ANDX Partnership Agreement), and recommended that the ANDX Board approve the Merger Agreement, the other transaction documents contemplated by the Merger Agreement (collectively, the “Transaction Documents”), and the consummation of the transactions contemplated thereby, including the Merger. Based on the approval and recommendation of the ANDX Conflicts Committee, the ANDX Board unanimously determined that the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger, are in, or not opposed to, the best interests of ANDX and its subsidiaries treated as a single consolidated entity, approved and declared advisable the Merger Agreement, the other Transaction Documents to which ANDX and ANDX GP are a party and the transactions contemplated thereby, including the Merger, recommended approval of the Merger Agreement and the Merger by the holders of ANDX Common Units and directed that the Merger Agreement be submitted to the holders of ANDX Common Units for their adoption by written consent.

The approval and adoption of the Merger Agreement and the Merger by ANDX require the affirmative vote or consent of (i) holders of at least a majority of the outstanding ANDX Common Units and (ii) ANDX GP and ANDX Refining Southwest, as holders of ANDX Common Units subject to the lower Affiliated Unitholder Exchange Ratio. Pursuant to the terms of a Support Agreement, dated as of May 7, 2019, by and among ANDX, ANDX GP, ANDX Refining Southwest, MPC and MPLX (the “Support Agreement”), ANDX GP and ANDX Refining Southwest, which, as of May 7, 2019, together beneficially owned 156,173,128 ANDX Common Units representing approximately 64% of the outstanding ANDX Common Units, agreed to deliver a written consent approving the Merger, the Merger Agreement and the transactions contemplated thereby (the “ANDX Written Consent”) within two business days after the effectiveness of the registration statement of which this consent statement/prospectus forms a part. The delivery of the ANDX Written Consent by ANDX GP and ANDX Refining Southwest with respect to the ANDX Common Units they own will be sufficient to adopt the Merger Agreement and thereby approve the Merger, without the receipt of written consent from any other holder of ANDX Common Units.

The ANDX Board has set June 28, 2019 as the record date (the “Record Date”) for determining the holders of ANDX Common Units entitled to execute and deliver written consents with respect to this consent statement/prospectus. If you are a record holder of outstanding ANDX Common Units as of the Record Date, you may complete, date and sign the enclosed written consent and promptly return it to ANDX. See the section entitled “Written Consents of Holders of ANDX Common Units” beginning on page 39 of this consent statement/prospectus.

This consent statement/prospectus provides you with detailed information about the proposed Merger and related matters. This represents a consent statement of ANDX in connection with the approval of the matters set forth herein, and a prospectus of MPLX in connection with the offering of the MPLX Common Units and MPLX Series B Preferred Units issuable in connection with the Merger. ANDX and MPLX encourage you to read the entire document carefully. In particular, please read the section entitled “Risk Factors” beginning on page 28 of this consent statement/prospectus for a discussion of risks relevant to the Merger and the combined partnership.

Sincerely,

Gary R. Heminger

Chairman of the Board and Chief Executive Officer

Tesoro Logistics GP, LLC, as the general partner

of Andeavor Logistics LP

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THE MERGER, THE ADOPTION OF THE MERGER AGREEMENT, THE ISSUANCE OF MPLX COMMON UNITS OR MPLX SERIES B PREFERRED UNITS IN CONNECTION WITH THE MERGER OR ANY OTHER TRANSACTIONS DESCRIBED IN THE ACCOMPANYING CONSENT STATEMENT/PROSPECTUS, OR PASSED UPON THE ADEQUACY OR ACCURACY OF THE DISCLOSURE IN THIS DOCUMENT. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

This consent statement/prospectus is dated June 28, 2019, and is first being mailed to unitholders on or about June 28, 2019.

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REFERENCES TO ADDITIONAL INFORMATION

This consent statement/prospectus incorporates important business and financial information about ANDX and MPLX from other documents that ANDX and MPLX have filed with the U.S. Securities and Exchange Commission (the “SEC”) and that are contained in or incorporated by reference herein. For a listing of documents incorporated by reference herein, please see the section entitled “Where You Can Find More Information” beginning on page 172. This information is available for you to review free of charge through the SEC’s website at www.sec.gov.

You may request copies of this consent statement/prospectus and any of the documents incorporated by reference herein or other information concerning ANDX or MPLX, without charge, upon written or oral request to the applicable company’s principal executive offices. The respective addresses and telephone numbers of such principal executive offices are listed below.

To obtain timely delivery of these documents prior to the conclusion of the consent process, holders of ANDX Common Units must request the information no later than July 22, 2019.

ABOUT THIS CONSENT STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by MPLX (File No. 333-231798), constitutes a prospectus of MPLX under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the MPLX Common Units and MPLX Series B Preferred Units to be issued to holders of ANDX Common Units (“ANDX Common Unitholders”) and holders of ANDX Series A Preferred Units (“ANDX Series A Preferred Unitholders” and, together with ANDX Common Unitholders, the “ANDX Unitholders”), respectively, pursuant to the Merger Agreement, as such agreement may be amended from time to time.

MPLX has supplied all information contained or incorporated by reference herein relating to MPLX, and ANDX has supplied all information contained or incorporated by reference herein relating to ANDX. MPLX and ANDX have both contributed to the information relating to the Merger contained in this consent statement/prospectus.

You should rely only on the information contained in or incorporated by reference herein in connection with the giving or withholding of any consent or any investment decision in connection with the Merger. MPLX and ANDX have not authorized anyone to provide you with information that is different from that contained or incorporated by reference herein. This consent statement/prospectus is dated June 28, 2019, and you should not assume that the information contained in this consent statement/prospectus is accurate as of any date other than such date unless otherwise specifically provided herein. Further, you should not assume that the information incorporated by reference herein is accurate as of any date other than the date of the incorporated document. Neither the mailing of this consent statement/prospectus to ANDX Common Unitholders and ANDX Series A Preferred Unitholders, nor the issuance by MPLX of MPLX Common Units or MPLX Series B Preferred Units pursuant to the Merger Agreement will create any implication to the contrary.

MPLX Common Units and ANDX Common Units are traded on the New York Stock Exchange (the “NYSE”) under the symbols “MPLX” and “ANDX”, respectively.

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QUESTIONS AND ANSWERS

The following section provides brief answers to certain questions that you may have regarding the Merger Agreement and the Merger. Please note that this section does not address all issues that may be important to you as an ANDX Common Unitholder or an ANDX Series A Preferred Unitholder. Accordingly, you should carefully read this entire consent statement/prospectus, including each of the annexes, and the documents that have been incorporated by reference into this consent statement/prospectus.

ANDX, MPLX and their general partners have agreed to combine the businesses of ANDX and MPLX by merging Merger Sub, a direct, wholly owned subsidiary of MPLX, with and into ANDX with ANDX being the surviving entity and becoming a direct, wholly owned subsidiary of MPLX. The approval and adoption of the Merger Agreement and the Merger by ANDX requires the affirmative vote or consent of (i) holders of at least a majority of the outstanding ANDX Common Units and (ii) ANDX GP and ANDX Refining Southwest, as holders of ANDX Common Units subject to the lower Affiliated Unitholder Exchange Ratio. If you are a record holder of outstanding ANDX Common Units as of the close of business on June 28, 2019 (the “Record Date”), you may complete, date and sign the enclosed written consent and promptly return it to ANDX. This consent statement/prospectus contains important information about the Merger Agreement, the Merger and the other actions contemplated thereby, and you should read this consent statement/prospectus carefully.

ANDX Series A Preferred Unitholders are receiving this consent statement/prospectus as information only.

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Each of ANDX GP and ANDX Refining Southwest will be entitled to receive MPLX Common Units in exchange for each such holder’s ANDX Common Units at the Affiliated Unitholder Exchange Ratio for ANDX Common Units held by each such holder that were issued and outstanding immediately prior to the effective time of the Merger.

If the Public Unitholder Exchange Ratio or Affiliated Unitholder Exchange Ratio would result in the ANDX Common Unitholder being entitled to receive, after combining all fractional units (rounded to three decimal places) to which such holder would otherwise be entitled to receive in connection with the Merger, a fraction of an MPLX Common Unit, such holder will receive cash (without interest, rounded to the nearest cent) in lieu of such fractional MPLX Common Unit in an amount equal to the product obtained by multiplying (i) the aggregated amount of the fractional interest in MPLX Common Units to which such holder would be entitled and (ii) an amount equal to the average of the volume weighted average price per unit of MPLX Common Units on the NYSE (as reported by Bloomberg L.P. or, if not reported therein, in another authoritative source mutually selected by MPLX and ANDX) on each of the ten consecutive trading days ending with the complete trading day immediately prior to the effective time of the Merger.

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For additional information regarding exchange procedures, please read the section entitled “The Merger Agreement—Exchange Procedures” beginning on page 82.

Each ANDX Phantom Unit, other than any ANDX Director Phantom Unit, whether vested or unvested, will be converted into a phantom unit denominated in MPLX Common Units (each, a “Converted MPLX Phantom Unit and, collectively, the “Converted MPLX Phantom Units”). The number of MPLX Common Units subject to each Converted MPLX Phantom Unit will be equal to the product (rounded down to the nearest whole number) of (x) the number of ANDX Common Units subject to such ANDX Phantom Unit immediately prior to the effective time of the Merger multiplied by (y) the Public Unitholder Exchange Ratio. Any then-accumulated distribution equivalent amounts payable pursuant to distribution equivalent rights with respect to each ANDX Phantom Unit will carry over and be paid to the holder upon the vesting of the Converted MPLX Phantom Unit that corresponds to the ANDX Phantom Unit to which such distribution equivalent amounts relate. Each ANDX Director Phantom Unit will be converted into the right to receive (without interest), as soon as reasonably practicable after the effective time of the Merger, a cash payment equal to (i) the number of ANDX Common Units subject to the ANDX Director Phantom Unit immediately prior to the effective time of the Merger, whether or not vested, multiplied by (ii) the product of (A) the Public Unitholder Exchange Ratio and (B) the average of the volume weighted average price per unit of MPLX Common Units on the NYSE (as reported by Bloomberg L.P. or, if not reported therein, in another authoritative source mutually selected by MPLX and ANDX) on each of the ten consecutive trading days ending with the complete trading day immediately prior to the closing date of the Merger (the “Closing Date”).

The ANDX Special Limited Partner Interest, as defined in the ANDX Partnership Agreement, outstanding immediately prior to the effective time of the Merger will be converted into the right to receive a new special limited partner interest in MPLX with substantially equivalent rights, powers, duties and obligations as the ANDX Special Limited Partner Interest (the “MPLX Special Limited Partner Interest”).

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Prior to the effective time of the Merger, subject to the coordination of distributions noted above, ANDX GP will determine, declare and cause ANDX to pay regular quarterly cash distributions on the ANDX Common Units for each quarter in accordance with the ANDX Partnership Agreement in the ordinary course and consistent with past practice, including with respect to amount and timing of record dates and payment dates; provided, however that, subject to applicable law, the coordination of distributions noted above and the ANDX Partnership Agreement, any such regular quarterly distribution will not be less than $1.03 per ANDX Common Unit without the separate determination and approval of the ANDX Conflicts Committee.

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RISK FACTORS

In addition to the other information contained in or incorporated by reference herein, including the matters addressed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 26, ANDX Common Unitholders should carefully consider the following risks before deciding whether to consent to the Merger. ANDX Common Unitholders should also consider the other information in this consent statement/prospectus and the other documents incorporated by reference herein, particularly the risk factors contained in MPLX’s and ANDX’s Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q. See the section entitled “Where You Can Find More Information” beginning on page 172.

Risks Relating to the Merger

The number of MPLX Common Units that holders of ANDX Common Units will be entitled to receive in the Merger is based upon a fixed Public Unitholder Exchange Ratio and Affiliated Unitholder Exchange Ratio. As a result, ANDX Common Unitholders cannot be certain of the precise value of the applicable merger consideration.

The Public Unitholder Exchange Ratio and Affiliated Unitholder Exchange Ratio are fixed, meaning that they do not change and are not dependent upon the relative values of MPLX Common Units and ANDX Common Units. There will be no adjustment to the Public Unitholder Exchange Ratio or Affiliated Unitholder Exchange Ratio for changes in the market price of MPLX Common Units or ANDX Common Units prior to the completion of the Merger. If the Merger is completed, there will be a time lapse between the date of this consent statement/prospectus and the date on which ANDX Unitholders entitled to receive the applicable merger consideration actually receive such applicable merger consideration. The market value of MPLX Common Units may fluctuate during and after these periods as a result of a variety of factors, including general market and economic conditions, changes in MPLX’s businesses, operations and prospects and regulatory considerations. Such factors are difficult to predict and in many cases may be beyond the control of MPLX and ANDX. Consequently, at the time ANDX Common Unitholders must decide whether to adopt the Merger Agreement, they will not know the actual market value of the applicable merger consideration they will receive when the Merger is completed. The actual value of the applicable merger consideration received by ANDX Common Unitholders at the completion of the Merger will depend on the market value of the MPLX Common Units at that time. This market value may differ, possibly materially, from the market value of MPLX Common Units at the time the Merger Agreement was entered into or at any other time. For additional information about the ANDX per unit applicable merger consideration, see the section entitled “The Merger Agreement—Merger Consideration” beginning on page 81.

The market price of MPLX Common Units will continue to fluctuate after the Merger.

Upon completion of the Merger, holders of ANDX Common Units will become holders of MPLX Common Units. The market price of MPLX Common Units may fluctuate significantly following completion of the Merger and holders of ANDX Common Units could lose some or all of the value of their investment in MPLX Common Units. In addition, the stock market has experienced significant price and volume fluctuations in recent times which, if they continue to occur, could have a material adverse effect on the market for, or liquidity of, the MPLX Common Units, regardless of MPLX’s actual operating performance.

The market price of MPLX Common Units may be affected by factors different from those that historically have affected the market price of ANDX Common Units.

Upon completion of the Merger, holders of ANDX Common Units will become holders of MPLX Common Units. The businesses of MPLX differ from those of ANDX in certain respects, and, accordingly, the financial position or results of operations and/or cash flows of MPLX after the Merger, as well as the market price of MPLX Common Units, may be affected by factors different from those currently affecting the financial position

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or results of operations and/or cash flows of ANDX. Following the completion of the Merger, ANDX will be part of a larger company with other lines of business and a broader geographic footprint, so decisions affecting ANDX may be made in respect of the larger combined business as a whole rather than the ANDX businesses individually. For a discussion of the businesses of MPLX and ANDX and of some important factors to consider in connection with those businesses, see the section entitled “Information About the Parties” beginning on page 37, and the documents incorporated by reference in the section entitled “Where You Can Find More Information” beginning on page 172, including, in particular, in the sections entitled “Risk Factors” in each of MPLX’s Annual Report on Form 10-K for the year ended December 31, 2018 and ANDX’s Annual Report on Form 10-K for the year ended December 31, 2018.

The Merger Agreement may be terminated in accordance with its terms and the Merger may not be completed.

The Merger Agreement is subject to a number of conditions that must be satisfied or waived in order to complete the Merger. Those conditions include, among others: adoption of the Merger Agreement by ANDX Common Unitholders, the accuracy of representations and warranties under the Merger Agreement (subject to the materiality standards set forth in the Merger Agreement) and MPLX’s and ANDX’s performance of their respective obligations under the Merger Agreement in all material respects. These conditions to the closing of the Merger may not be fulfilled in a timely manner or at all, and, accordingly, the Merger may be delayed or may not be completed.

In addition, if the Merger is not completed by November 8, 2019, either MPLX or ANDX may choose not to proceed with the Merger, and the parties can mutually decide to terminate the Merger Agreement at any time. In addition, MPLX and ANDX may elect to terminate the Merger Agreement in certain other circumstances. See the section entitled “The Merger Agreement—Termination” beginning on page 96.

Failure to complete the Merger could negatively impact the price of MPLX Common Units and the price of ANDX Common Units, as well as MPLX’s and ANDX’s respective future businesses and financial results.

If the Merger is not completed for any reason, MPLX’s and ANDX’s respective businesses and financial results may be adversely affected as follows:

MPLX Unitholders and ANDX Unitholders will have a reduced ownership in the combined partnership as compared to their ownership in MPLX and ANDX, respectively, prior to the Merger.

At the effective time of the Merger, each ANDX Common Unitholder that receives MPLX Common Units will become an MPLX Common Unitholder, with a percentage of ownership of MPLX that is smaller than such unitholder’s percentage ownership in ANDX prior to the Merger. Following the completion of the Merger, the former holders of ANDX Common Units are estimated to own approximately 25% of the outstanding MPLX Common Units immediately after the Merger and current holders of MPLX Common Units as a group are estimated to own approximately 75% of the outstanding MPLX Common Units immediately after the Merger.

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The number of outstanding MPLX Common Units will increase and MPLX will have outstanding an additional class of preferred units as a result of the Merger, which could make it more difficult for MPLX to pay the current level of quarterly distributions.

As of June 21, 2019, there were approximately 794,349,619 MPLX Common Units outstanding. MPLX anticipates that it will issue approximately 263 million MPLX Common Units in connection with the Merger. Accordingly, the aggregate dollar amount required to pay the current per unit quarterly distribution on all MPLX Common Units will increase, which could increase the likelihood that MPLX will not have sufficient funds to pay the current level of quarterly distributions to all MPLX Unitholders. Using a $0.6575 per MPLX Common Unit distribution (the amount MPLX paid with respect to the first fiscal quarter of 2019 on May 15, 2019), the aggregate cash distribution paid to MPLX Unitholders on MPLX Common Units totaled approximately $523 million, including a distribution of approximately $332 million to wholly owned subsidiaries of MPC in respect of MPLX Common Units owned by them. Using the same $0.6575 per MPLX Common Unit distribution, the combined pro forma MPLX distribution with respect to the first fiscal quarter of 2019, had the Merger been completed prior to such distribution and giving effect to the ANDX distribution waiver in effect, would have resulted in total cash distributions of approximately $683 million, including a distribution of approximately $425 million to wholly owned subsidiaries of MPC in respect of MPLX Common Units owned by them.

Further, MPLX will issue 600,000 new MPLX Series B Preferred Units in the Merger. MPLX must pay distributions that have accrued on the MPLX Series A Preferred Units and the new MPLX Series B Preferred Units prior to paying any distributions on the MPLX Common Units. Distributions are payable on the MPLX Series A Preferred Units at a rate of the greater of $0.528125 per quarter per MPLX Series A Preferred Unit or the quarterly distribution that the holder would have received on an as-converted basis. MPLX paid approximately $20 million in distributions on the MPLX Series A Preferred Units for the first quarter of 2019. Distributions will initially accrue on the MPLX Series B Preferred Units at a rate of $68.75 per unit per annum, payable on a semi-annual basis, which amounts to total annual distributions of approximately $41 million. The requirement to pay distributions on the new MPLX Series B Preferred Units increases the likelihood that MPLX will not have sufficient funds to pay the current level of distributions to the holders of MPLX Common Units following the completion of the Merger.

A downgrade in MPLX’s credit ratings following the Merger could impact the combined partnership’s access to capital and costs of doing business, and independent third parties control and maintain its credit ratings.

Following the Merger, MPLX will have more debt outstanding on a consolidated basis than it has prior to the Merger, and the Merger may cause rating agencies to reevaluate MPLX’s ratings. A downgrade of MPLX’s credit ratings might increase MPLX’s cost of borrowing and could require MPLX to post collateral with third parties, negatively impacting its available liquidity. MPLX’s ability to access capital markets could also be limited by a downgrade of its credit ratings and other disruptions.

Credit rating agencies perform independent analysis when assigning credit ratings. The analysis includes a number of criteria including, but not limited to, business composition, market and operational risks, as well as various financial tests. Credit rating agencies continue to review the criteria for industry sectors and various debt ratings and may make changes to those criteria from time to time. Credit ratings are not recommendations to buy, sell or hold investments in the rated entity. Ratings are subject to revision or withdrawal at any time by the rating agencies, and MPLX cannot assure that it will maintain its current credit ratings.

The Merger is subject to conditions, including certain conditions that may not be satisfied, or completed on a timely basis, if at all.

The Merger is subject to a number of conditions beyond ANDX’s and MPLX’s control that may prevent, delay or otherwise materially adversely affect its completion. Neither MPLX nor ANDX can predict whether and when these other conditions will be satisfied. Any delay in completing the Merger could cause the combined

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partnership not to realize some or all of the synergies expected to be achieved if the Merger is successfully completed within its expected time frame. Please see the section entitled “The Merger Agreement—Conditions to the Completion of the Merger” beginning on page 94.

MPLX and ANDX will be subject to business uncertainties while the Merger is pending, which could adversely affect their respective businesses.

Uncertainty about the effect of the Merger on employees and customers may have an adverse effect on MPLX and ANDX. These uncertainties could cause customers and others that deal with MPLX and ANDX to seek to change their existing business relationships with MPLX and ANDX, respectively. Retaining employees who provide services to the partnerships may be particularly challenging during the pendency of the Merger, as they may experience uncertainty about their roles with the combined partnership following the Merger. In addition, the Merger Agreement restricts MPLX and ANDX from entering into certain corporate transactions and taking other specified actions without the consent of the other party, and generally requires ANDX to continue its operations in the ordinary course, until completion of the Merger. These restrictions may prevent MPLX and ANDX from pursuing attractive business opportunities that may arise prior to the completion of the Merger. Please see the section entitled “The Merger Agreement—Interim Operations of MPLX and ANDX Pending the Merger,” beginning on page 89, for a description of the restrictive covenants to which MPLX and ANDX are subject.

Directors and executive officers of ANDX GP may have interests in the Merger that are different from, or in addition to, the interests of ANDX Unitholders.

Directors and executive officers of ANDX GP may have interests in the Merger and related transactions, that are different from, or in addition to, the interests of ANDX Unitholders generally. With respect to at least some of the directors and executive officers of ANDX GP, these interests include, among others, positions as directors or officers of MPC, MPLX GP and their respective affiliates; equity holdings in MPC or MPLX; the treatment of outstanding equity-based awards pursuant to the Merger Agreement; and rights to ongoing indemnification and insurance coverage.

These interests are described in more detail in the section entitled “The Merger—Interests of Directors and Executive Officers of ANDX GP in the Merger” beginning on page 73.

A lawsuit has been filed challenging the adequacy of the disclosures made in the registration statement of which this consent statement/prospectus forms a part and an adverse ruling in this lawsuit may prevent the Merger from being completed.

On June 19, 2019, a purported ANDX Common Unitholder filed a complaint in the United States District Court of the Southern District of New York, alleging that ANDX and the directors of ANDX GP disseminated a registration statement regarding the proposed Merger in violation of Section 14(a) of the Exchange Act and SEC Rule 14a-9 promulgated thereunder because it omits material information with respect to the Merger and further alleges that the directors of ANDX are liable for these violations as “controlling persons” of ANDX under Section 20(a) of the Exchange Act.

Additional lawsuits arising out of the Merger may be filed in the future. There can be no assurance that any of the defendants will be successful in the outcome of the pending or any potential future lawsuits. A preliminary injunction could delay or jeopardize the completion of the Merger, and an adverse judgment granting permanent injunctive relief could indefinitely enjoin the completion of the Merger.

The Merger may not be accretive, and may be dilutive, to MPLX’s earnings per unit, which may negatively affect the market price of MPLX Common Units.

In connection with the completion of the Merger, based on the number of issued and outstanding ANDX Common Units as of June 21, 2019, MPLX will issue up to approximately 263 million MPLX Common Units. Additionally, approximately 0.2 million MPLX Common Units are expected to be subject to Converted MPLX

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Phantom Units following the Merger. The issuance of these new MPLX Common Units could have the effect of depressing the market price of MPLX Common Units, through dilution of earnings per unit or otherwise. Any dilution of, or delay of any accretion to, MPLX earnings per unit could cause the price of MPLX Common Units to decline or increase at a reduced rate.

MPLX and ANDX will incur significant transaction and Merger-related costs in connection with the Merger, which may be in excess of those anticipated by MPLX and ANDX.

Each of MPLX and ANDX has incurred and will incur substantial expenses in connection with the negotiation and completion of the transactions contemplated by the Merger Agreement, including the costs and expenses of filing, printing and mailing this consent statement/prospectus and all filing and other fees paid to the SEC in connection with the Merger.

MPLX and ANDX expect to continue to incur a number of non-recurring costs associated with completing the Merger, combining the operations of the two partnerships and achieving desired synergies. These fees and costs have been, and will continue to be, substantial. The substantial majority of non-recurring expenses will consist of transaction costs related to the Merger and include, among others, employee retention costs, fees paid to financial, legal and accounting advisors, severance and benefit costs and filing fees.

MPLX and ANDX will also incur transaction fees and costs related to formulating and implementing integration plans, including facilities and systems consolidation costs. MPLX and ANDX will continue to assess the magnitude of these costs, and additional unanticipated costs may be incurred in the Merger and the integration of the two partnerships’ businesses. Although MPLX and ANDX each expects that the elimination of duplicative costs, as well as the realization of other efficiencies related to the integration of the businesses, should allow MPLX and ANDX to offset integration-related costs over time, this net benefit may not be achieved in the near term, or at all. See the risk factor entitled “The integration of MPLX and ANDX may not be as successful as anticipated” below.

The costs described above, as well as other unanticipated costs and expenses, could have a material adverse effect on the financial condition and operating results of MPLX following the completion of the Merger.

Many of these costs will be borne by MPLX and/or ANDX even if the Merger is not completed.

The unaudited pro forma condensed combined financial statements and unaudited forecasted financial information included in this consent statement/prospectus are presented for illustrative purposes only and do not represent the actual financial position or results of operations of the combined partnership following the Merger.

The unaudited pro forma condensed combined financial statements and unaudited forecasted financial information contained in this consent statement/prospectus are presented for illustrative purposes only, contain a variety of adjustments, assumptions and preliminary estimates and do not represent the actual financial position or results of operations of MPLX and ANDX prior to the Merger or that of the combined partnership following the Merger for several reasons. See the section entitled “Unaudited Pro Forma Condensed Combined Financial Statements” beginning on page 126. In addition, the Merger and post-Merger integration process may give rise to unexpected liabilities and costs, including costs associated with the defense and resolution of transaction-related litigation or other claims. Unexpected delays in completing the Merger or in connection with the post-Merger integration process may significantly increase the related costs and expenses incurred by MPLX. The actual financial positions and results of operations of MPLX and ANDX prior to the Merger and that of the combined partnership following the Merger may be different, possibly materially, from the unaudited pro forma condensed combined financial statements or forecasted financial information included in this consent statement/prospectus. In addition, the assumptions used in preparing the unaudited pro forma condensed combined financial statements and forecasted financial information included in this consent statement/prospectus may not prove to be accurate

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and may be affected by other factors. Any significant changes in the market price of MPLX Common Units may cause a significant change in the purchase price used for MPLX’s accounting purposes and the unaudited pro forma financial statements contained in this consent statement/prospectus.

The integration of MPLX and ANDX may not be as successful as anticipated.

The Merger involves numerous operational, strategic, financial, accounting, legal, tax and other risks; potential liabilities associated with the acquired businesses; and uncertainties related to design, operation and integration of ANDX’s internal control over financial reporting. Difficulties in integrating MPLX and ANDX may result in ANDX performing differently than expected, in operational challenges or in the failure to realize anticipated efficiencies. MPLX’s and ANDX’s existing businesses could also be negatively impacted by the Merger. Potential difficulties that may be encountered in the integration process include, among other factors:

Even if MPLX and ANDX complete the Merger, MPLX may fail to realize all of the anticipated benefits of the proposed Merger.

The success of the proposed Merger will depend, in part, on MPLX’s ability to realize the anticipated benefits and cost savings from combining MPLX’s and ANDX’s businesses. The anticipated benefits and cost savings of the proposed Merger may not be realized fully or at all, or may take longer to realize than expected or could have other adverse effects that MPLX does not currently foresee. Some of the assumptions that MPLX has made, such as the achievement of operating synergies and the expansion in opportunities for logistics growth in crude oil production basins and regions, may not be realized. The integration process may, for each of MPLX and ANDX, result in the loss of key personnel who provide services to the two partnerships, the disruption of ongoing businesses or inconsistencies in standards, controls, procedures and policies. There could be potential unknown liabilities and unforeseen expenses associated with the Merger that were not discovered in the course of performing due diligence.

The market price of MPLX Common Units may decline in the future as a result of the sale of MPLX Common Units held by former ANDX Unitholders or current MPLX Unitholders.

Following their receipt of MPLX Common Units as consideration in the Merger, former ANDX Common Unitholders may seek to sell the MPLX Common Units delivered to them. Other MPLX Common Unitholders may also seek to sell MPLX Common Units held by them following, or in anticipation of, completion of the Merger. These sales (or the perception that these sales may occur), coupled with the increase in the outstanding number of MPLX Common Units, may affect the market for, and the market price of, MPLX Common Units in an adverse manner.

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The combined partnership will record goodwill and other intangible assets that could become impaired and result in material non-cash charges to the results of operations of the combined partnership in the future.

The Merger will be accounted for as a reorganization of entities under common control in accordance with accounting principles generally accepted in the United States. Under a reorganization of entities under common control, the assets and liabilities of ANDX transferred between entities under common control will be recorded by MPLX based on MPC’s historical cost basis resulting from its preliminary purchase price accounting. MPLX will record ANDX’s assets and liabilities at MPC’s basis as of October 1, 2018, the date that common control was first established. See the section entitled “Unaudited Pro Forma Condensed Combined Financial Statements” beginning on page 126.

Effective October 1, 2018, MPC acquired Andeavor, including a controlling interest in ANDX, thus establishing common control between MPLX, ANDX, MPLX GP and ANDX GP. Under MPC’s application of the acquisition method of accounting, a portion of the total purchase price was allocated to ANDX’s tangible assets and liabilities and identifiable intangible assets based on their fair values as of October 1, 2018. The excess of the allocated purchase price over those fair values was recorded as goodwill. MPC’s basis in ANDX’s tangible assets, liabilities, identifiable intangible assets and goodwill will be transferred to MPLX upon completion of the Merger. To the extent the value of goodwill or intangible assets becomes impaired, the combined partnership may be required to incur material non-cash charges relating to such impairment. The combined partnership’s operating results may be significantly impacted from both the impairment and the underlying trends in the business that triggered the impairment.

ANDX Unitholders will have different rights as MPLX Unitholders under the MPLX Partnership Agreement than they currently have as ANDX Unitholders under the ANDX Partnership Agreement.

Upon completion of the Merger, ANDX Unitholders will become MPLX Unitholders and their rights will be governed by the MPLX Partnership Agreement. There are certain differences between the current rights of ANDX Unitholders under the ANDX Partnership Agreement and the rights to which they will be entitled to as MPLX Unitholders under the MPLX Partnership Agreement. See the sections entitled “Comparison of Unitholders’ Rights” and “Comparison of Preferred Unitholders’ Rights” beginning on pages 139 and 160, respectively, for a comparison of unitholder rights under the ANDX Partnership Agreement and the MPLX Partnership Agreement.

Tax Risks of the Merger

No ruling has been obtained with respect to the U.S. federal income tax consequences of the Merger.

No ruling has been or will be requested from the Internal Revenue Service (the “IRS”) with respect to the U.S. federal income tax consequences of the Merger. Please read the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 99.

The expected U.S. federal income tax consequences of the Merger are dependent upon MPLX and ANDX being treated as partnerships for U.S. federal income tax purposes.

The treatment of the Merger as nontaxable to ANDX Unitholders is dependent upon MPLX and ANDX each being treated as a partnership for U.S. federal income tax purposes. If MPLX or ANDX were treated as a corporation for U.S. federal income tax purposes, the consequences of the Merger would be materially different and the Merger would likely be a fully taxable transaction to ANDX Unitholders. For additional information, please read the section entitled “Material U.S. Federal Income Tax Consequences of the Merger—Assumptions Related to the U.S. Federal Income Tax Treatment of the Merger” beginning on page 100.

ANDX Unitholders could recognize taxable income or gain for U.S. federal income tax purposes, in certain circumstances, as a result of the Merger.

For U.S. federal income tax purposes, (1) ANDX will be deemed to contribute all of its assets to MPLX in exchange for (i) MPLX Common Units, MPLX Series B Preferred Units, MPLX TexNew Mex Units and the

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MPLX Special Limited Partner Interest, (ii) the assumption of ANDX’s liabilities, and (iii) cash received in lieu of fractional MPLX Common Units, followed by (2) a liquidation of ANDX in which (i) MPLX Common Units and cash are distributed to the ANDX Common Unitholders, (ii) MPLX Series B Preferred Units are distributed to the holders of the ANDX Series A Preferred Units, (iii) MPLX TexNew Mex Units are distributed to the holder of ANDX TexNew Mex Units, and (iv) the MPLX Special Limited Partner Interest is distributed to the holder of the ANDX Special Limited Partner Interest. The actual receipt of cash and the deemed receipt of cash by ANDX in the Merger could trigger gain to ANDX either because it would be treated as part of a sale or because it exceeds ANDX’s adjusted tax basis in its assets at the closing of the Merger, and any such gain would be allocated to the ANDX Unitholders pursuant to the ANDX Partnership Agreement. ANDX expects that the actual receipt of cash and the deemed receipt of cash by ANDX will qualify for one or more exceptions to sale treatment and ANDX does not currently expect that it will recognize gain as a result of the deemed receipt of cash in the Merger exceeding its adjusted tax basis in its assets. Please read the section entitled “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to ANDX” beginning on page 101.

In addition, as a result of the Merger, ANDX Common Unitholders who receive MPLX Common Units will become limited partners of MPLX for U.S. federal income tax purposes and will be allocated a share of MPLX’s nonrecourse liabilities. Each ANDX Common Unitholder will be treated as receiving a deemed cash distribution equal to the excess, if any, of such ANDX Common Unitholder’s share of nonrecourse liabilities of ANDX immediately before the Merger over such ANDX Common Unitholder’s share of nonrecourse liabilities of MPLX immediately following the Merger. If the amount of cash actually received in the Merger plus any deemed cash distribution received by such ANDX Common Unitholder exceeds the ANDX Common Unitholder’s basis in his ANDX Common Units, such ANDX Common Unitholder will recognize gain in an amount equal to such excess. While there can be no assurance, MPLX and ANDX expect that most ANDX Common Unitholders will not recognize gain in this manner. ANDX Series A Preferred Unitholders will not recognize gain in this manner, as ANDX Series A Preferred Unitholders are not allocated any share of ANDX’s nonrecourse liabilities and, as holders of MPLX Series B Preferred Units, will not be allocated any share of MPLX’s nonrecourse liabilities.

Further, the contribution of property or cash by a partner to a partnership in exchange for a new or additional interest in such partnership will generally not result in the recognition of gain or loss by such partner. However, under Section 707 of the Code and the Treasury Regulations promulgated thereunder, a contribution of cash or other property by a partner to a partnership and a transfer of property (other than an interest in such partnership) by the partnership to such partner, may, in certain circumstances, be characterized, in whole or in part, as a “disguised sale” of property by the partnership to the partner, rather than as a non-taxable distribution of such property by the partnership. For example, if a partner contributes cash to a partnership, and within a reasonable period of time before or after the contribution receives a distribution of property (other than an interest in such partnership) with a value approximately equal to the cash contributed, the transfers may be treated as part of a disguised sale of the distributed property. As a result, contributions of cash or other property to ANDX after the date of the Merger Agreement and prior to the effective time of the Merger may be treated as part of a “disguised sale” of a portion of the MPLX Common Units received in the Merger and may result in gain to ANDX. Any such taxable gain recognized by ANDX as part of a “disguised sale” would be allocated to the ANDX Common Unitholders pursuant to the ANDX Partnership Agreement.

Moreover, each ANDX Common Unitholder holding ANDX Common Units outstanding immediately prior to the effective time of the Merger will be entitled to receive MPLX Common Units in the Merger in exchange for such holder’s ANDX Common Units at the Public Unitholder Exchange Ratio or the Affiliated Unitholder Exchange Ratio, as applicable. As a result, there is a risk that public holders of ANDX Common Units could be deemed, for U.S. federal income tax purposes, to have received non-pro rata merger consideration, which could be taxable to such holders. ANDX will specially allocate unrealized gain and loss to the capital accounts of ANDX Common Unitholders in an effort to achieve relative capital accounts consistent with the Public Unitholder Exchange Ratio and the Affiliated Unitholder Exchange Ratio. In the event such allocations are insufficient, ANDX may specially allocate gross income and loss to achieve capital accounts consistent with the

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applicable exchange ratio. Although unlikely, other characterizations are possible, and the IRS could take the position that a public holder of ANDX Common Units is required to recognize taxable income with respect to any excess consideration such holder is deemed to receive in the Merger. For additional information, please read the section entitled “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to ANDX Unitholders” beginning on page 102.

The amount and effect of any gain that may be recognized for ANDX Unitholders will depend on such ANDX Unitholder’s particular situation, including the ability of such ANDX Unitholder to utilize any suspended passive losses. ANDX Unitholders are urged to consult their tax advisor for a full understanding of the U.S. federal, state, local and foreign tax consequences of the Merger to them. For additional information, please read the sections entitled “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to ANDX” and “Material U.S. Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to ANDX Unitholders” beginning on pages 101 and 102, respectively.

Tax Risks of Holding MPLX Units

You should read and consider risk factors specific to holding MPLX units that will also affect ANDX Unitholders after the completion of the Merger. These risks are described in Part I, Item 1A of MPLX’s Annual Report on Form 10-K for the year ended December 31, 2018, and in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 172 for the location of information incorporated by reference in this consent statement/prospectus.

Treatment of preferred distributions as guaranteed payments for the use of capital creates a different tax treatment for the holders of the MPLX Series B Preferred Units than the holders of MPLX Common Units

The tax treatment of distributions on the MPLX Series B Preferred Units is uncertain. MPLX will treat the holders of such MPLX Series B Preferred Units as partners for tax purposes and will treat distributions on those MPLX Series B Preferred Units as guaranteed payments for the use of capital that will generally be taxable to the holders of the MPLX Series B Preferred Units as ordinary income. This is consistent with the historical treatment by ANDX of the holders of ANDX Series A Preferred Units that are receiving the MPLX Series B Preferred Units in the Merger. Although a holder of MPLX Series B Preferred Units could recognize taxable income from the accrual of such a guaranteed payment even in the absence of a contemporaneous distribution, MPLX anticipates accruing and making the distributions on such units semi-annually or quarterly, as applicable. The holders of the MPLX Series B Preferred Units are generally not anticipated to share in the partnership’s items of income, gain, loss or deduction, except to the extent necessary to provide, to the extent possible, the MPLX Series B Preferred Units with the benefit of their liquidation preference.

Risks Relating to MPLX’s Business

You should read and consider risk factors specific to MPLX businesses that will also affect the combined partnership after the completion of the Merger. These risks are described in Part I, Item 1A of MPLX’s Annual Report on Form 10-K for the year ended December 31, 2018, and in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 172 for the location of information incorporated by reference in this consent statement/prospectus.

Risks Relating to ANDX’s Business

You should read and consider risk factors specific to ANDX’s businesses that will also affect the combined partnership after the completion of the Merger. These risks are described in Part I, Item 1A of ANDX’s Annual Report on Form 10-K for the year ended December 31, 2018, and in other documents that are incorporated by reference herein. See the section entitled “Where You Can Find More Information” beginning on page 172 for the location of information incorporated by reference in this consent statement/prospectus.

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INFORMATION ABOUT THE PARTIES

ANDEAVOR LOGISTICS LP

200 East Hardin Street

Findlay, Ohio 45840

Phone: 419-421-2414

ANDX is a fee-based, full-service, diversified midstream logistics company with integrated assets across the western and mid-continent regions of the United States. ANDX was formed by Andeavor and its wholly owned subsidiary, ANDX GP, in 2010 as a Delaware master limited partnership to own, operate, develop and acquire logistics assets. ANDX operates through three business segments: Terminalling and Transportation, Gathering and Processing and Wholesale. The Terminalling and Transportation segment consists of marine terminals, refined product truck terminals, rail terminals, dedicated storage facilities and transportation pipelines. The Gathering and Processing segment consists of crude oil gathering systems and pipelines as well as natural gas gathering pipelines, processing facilities and fractionation facilities. The Wholesale segment consists of a fee-based fuel wholesale business. ANDX is headquartered in Findlay, Ohio. On October 1, 2018, MPC completed its acquisition of Andeavor in accordance with the Agreement and Plan of Merger, dated as of April 29, 2018, as amended, under which MPC acquired Andeavor. MPC controls ANDX through its indirect ownership of 100% of the membership interests of ANDX GP. MPC also indirectly owned approximately 64% of the outstanding ANDX Common Units as of June 21, 2019.

TESORO LOGISTICS GP, LLC

200 East Hardin Street

Findlay, Ohio 45840

Phone: 419-421-2414

ANDX GP is a Delaware limited liability company, an indirect, wholly owned subsidiary of MPC and owns the non-economic general partner interest in ANDX.

MPLX LP

200 East Hardin Street

Findlay, Ohio 45840

Phone: 419-421-2414

MPLX is a diversified, large-cap master limited partnership formed in 2012 by MPC. MPLX owns and operates midstream energy infrastructure and logistics assets and provides fuels distribution services. MPLX’s assets include a network of crude oil and refined product pipelines; an inland marine business; light-product terminals; storage caverns; refinery tanks, docks, loading racks, and associated piping; and crude and light-product marine terminals. MPLX also owns crude oil and natural gas gathering systems and pipelines as well as natural gas and NGL processing and fractionation facilities in key U.S. supply basins. MPLX’s operations are conducted in the following operating segments: L&S and G&P. MPLX’s L&S assets are primarily located in the Midwest and Gulf Coast regions of the U.S. while its G&P assets are primarily located in the Northeast and Southwest regions of the U.S. MPC controls MPLX through its indirect ownership of 100% of the membership interests of MPLX GP. MPC also indirectly owned approximately 64% of the outstanding MPLX Common Units as of June 21, 2019.

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MPLX GP LLC

200 East Hardin Street

Findlay, Ohio 45840

Phone: 419-421-2414

MPLX GP is a Delaware limited liability company, an indirect, wholly owned subsidiary of MPC and owns the non-economic general partner interest in MPLX.

MPLX MAX LLC

200 East Hardin Street

Findlay, Ohio 45840

Phone: 419-421-2414

Merger Sub is a direct, wholly owned subsidiary of MPLX. Upon the completion of the Merger, Merger Sub will cease to exist. Merger Sub was formed in Delaware on May 7, 2019 for the sole purpose of effecting the Merger.

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WRITTEN CONSENTS OF HOLDERS OF ANDX COMMON UNITS

ANDX Common Units Entitled to Consent and Consent Required

Only holders of ANDX Common Units of record at the close of business on the Record Date will be notified of and be entitled to execute and deliver a written consent with respect to the Merger Agreement, the Merger and on a non-binding, advisory basis, the compensation payments that will or may be made to certain of ANDX’s named executive officers in connection with the Merger (the “Non-Binding Compensation Advisory Proposal”).

Approval of the Merger Agreement and the Transactions Contemplated Thereby, Including the Merger

The approval and adoption of the Merger Agreement and the transactions contemplated thereby, including the Merger, by ANDX requires the affirmative vote or consent of (i) holders of at least a majority of the outstanding ANDX Common Units and (ii) ANDX GP and ANDX Refining Southwest, as holders of ANDX Common Units subject to the lower Affiliated Unitholder Exchange Ratio.

Pursuant to the terms of the Support Agreement, ANDX GP and ANDX Refining Southwest, which as of the Record Date together beneficially owned 156,173,128 ANDX Common Units, representing approximately 64% of the outstanding ANDX Common Units, have agreed to deliver the ANDX Written Consent within two business days after the effectiveness of the registration statement of which this consent statement/prospectus forms a part. The delivery of the ANDX Written Consent by ANDX GP and ANDX Refining Southwest with respect to the ANDX Common Units they own will be sufficient to adopt the Merger Agreement and thereby approve the Merger, without the receipt of written consent from any other ANDX Common Unitholder.

In addition, approval and adoption of the Merger Agreement and the Merger does not require the vote or consent of any other limited partners of ANDX pursuant to the terms of the ANDX Partnership Agreement.

Approval of the Non-Binding Compensation Advisory Proposal

Section 14A of the Exchange Act and the applicable SEC rules issued thereunder, which were enacted as part of the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010, require that ANDX provide its Common Unitholders with the opportunity to vote to approve, on an advisory (non-binding) basis, the compensation that may be paid or become payable to ANDX’s named executive officers in connection with the Merger, as disclosed in this consent statement/prospectus, including the compensation table and the related narrative named executive officer compensation disclosures set forth in “The Merger—Merger-Related Compensation” beginning on page 77. This vote is commonly referred to as a “golden parachute say on pay” vote. Accordingly, ANDX’s Common Unitholders are being provided with the opportunity to give their consent, on an advisory basis, on those potential payments.

The affirmative vote of the holders of a majority of the outstanding ANDX Common Units entitled to vote on the Non-Binding Compensation Advisory Proposal, is required to approve the Non-Binding Compensation Advisory Proposal.

The proposal to approve the Non-Binding Compensation Advisory Proposal is a vote separate and apart from the consent to approve the Merger Agreement and the Merger. Accordingly, an ANDX Common Unitholder may give consent with respect to one proposal and not the other. While the ANDX Board intends to consider the vote resulting from this proposal, the vote is advisory only and therefore not binding on ANDX. If the Merger is approved by holders of ANDX Common Units and consummated, the compensation will be payable even if the Non-Binding Compensation Advisory Proposal is not approved because such compensation is based on the terms of the Merger Agreement as well as the contractual arrangements with ANDX’s named

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executive officers. The delivery of the ANDX Written Consent by ANDX GP and ANDX Refining Southwest with respect to the ANDX Common Units they own will be sufficient to approve the Non-Binding Compensation Advisory Proposal, without the receipt of written consent from any other ANDX Common Unitholder.

ANDX is seeking approval of the following resolution by way of consent:

“RESOLVED, that ANDX’s Common Unitholders approve, on an advisory (non-binding) basis, the compensation that may be paid or become payable to ANDX’s named executive officers in connection with the Merger, as disclosed pursuant to Item 402(t) of Regulation S-K under the heading “The Merger—Merger-Related Compensation” (which disclosure includes the compensation table and related narrative named executive officer compensation disclosures required pursuant to Item 402(t) of Regulation S-K).”

Submission of Consents

Holders of ANDX Common Units may consent to the approval and adoption of the Merger Agreement, the Merger and the Non-Binding Compensation Advisory Proposal with respect to their ANDX Common Units by completing, dating and signing the written consent furnished with this consent statement/prospectus and returning it to ANDX.

If you hold ANDX Common Units as of the Record Date and you wish to give your written consent, you must fill out the enclosed written consent, date and sign it, and promptly return it to ANDX. Once you have completed, dated and signed the written consent, you may deliver it to ANDX by faxing it to Andeavor Logistics LP, Attention: Molly R. Benson, Secretary, at (419) 421-8427, by emailing a .pdf copy of your written consent to OfficeoftheSecretary@marathonpetroleum.com or by mailing your written consent to Andeavor Logistics LP at 200 East Hardin Street, Findlay, Ohio 45840, Attention: Molly R. Benson, Secretary. If you do not return your written consent, it will have the same effect as a vote against the approval and adoption of the Merger Agreement, the transactions contemplated thereby and the Non-Binding Compensation Advisory Proposal.

If you hold ANDX Common Units in “street name” with a bank, brokerage firm or other nominee, you should follow the instructions provided by your bank, brokerage firm or other nominee.

Upon the later of 20 business days after this consent statement/prospectus is sent to ANDX Unitholders and the date on which a sufficient number of consents to approve and adopt the Merger Agreement and the transactions contemplated thereby have been received, the consent process will conclude. The delivery of the ANDX Written Consent by ANDX GP and ANDX Refining Southwest with respect to the ANDX Common Units they own will be sufficient to adopt the Merger Agreement, and thereby approve the Merger, without the receipt of written consent from any other ANDX Common Unitholder.

Revocation of Consents

Your consent may be revoked at any time before the later of (i) 20 business days after this consent statement/prospectus is sent to ANDX Unitholders and (ii) the date on which the consents of a sufficient number of holders of ANDX Common Units (the “ANDX Common Unitholders”) to approve and adopt the Merger Agreement and the transactions contemplated thereby have been delivered to the secretary of ANDX. If you wish to revoke a previously given consent before that time, you may do so by faxing such revocation to Andeavor Logistics LP, Attention: Molly R. Benson, Secretary, at (419) 421-8427, by emailing a .pdf copy of such revocation to OfficeoftheSecretary@marathonpetroleum.com or by mailing such revocation to Andeavor Logistics LP at 200 East Hardin Street, Findlay, Ohio 45840, Attention: Molly R. Benson, Secretary.

Expenses

The expense of preparing, printing and mailing these consent materials is being borne equally by MPLX and ANDX.

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THE MERGER

This discussion of the Merger is qualified in its entirety by reference to the Merger Agreement, which is attached to this consent statement/prospectus as Annex A and incorporated by reference herein in its entirety. You should read the entire Merger Agreement carefully as it is the legal document that governs the Merger.

Transaction Structure

At the effective time of the Merger, Merger Sub will merge with and into ANDX. As a result of the Merger, the separate existence of Merger Sub will cease, and ANDX will continue as the surviving entity and a wholly owned subsidiary of MPLX.

Consideration to ANDX Common Unitholders

As a result of the Merger, each ANDX Common Unit, other than any ANDX Common Unit held by ANDX GP and ANDX Refining Southwest, issued and outstanding immediately prior to the effective time of the Merger will be converted into 1.135 validly issued, fully paid and non-assessable (except to the extent such non-assessability may be affected by Sections 17-303, 17-607 and 17-804 of the Delaware Revised Uniform Limited Partnership Act (the “DRULPA”)) MPLX Common Units.

As a result of the Merger, each ANDX Common Unit held by ANDX GP and ANDX Refining Southwest issued and outstanding immediately prior to the effective time of the Merger (“Affiliated Unitholder Eligible Units”) will be converted into 1.0328 validly issued, fully paid and non-assessable (except to the extent such non-assessability may be affected by Sections 17-303, 17-607 and 17-804 of the DRULPA) MPLX Common Units.

Holders of ANDX Common Units will not be entitled to receive any fractional MPLX Common Units in the Merger, and no holders of Public Unitholder Eligible Units or Affiliated Unitholder Eligible Units will be entitled to distributions, voting rights or other rights in respect of any fractional MPLX Common Unit. Holders of ANDX Common Units that would otherwise have been entitled to receive a fractional MPLX Common Unit will instead be entitled to receive, in lieu of fractional units, an amount in cash, without interest, rounded to the nearest cent, equal to the product of (A) the fraction of an MPLX Common Unit (after aggregating all the fractional MPLX Common Units held by the holder at the effective time of the Merger and rounded to three decimal places) to which the holder would otherwise be entitled, and (B) an amount equal to the average of the volume weighted average price per unit of the MPLX Common Units on the NYSE (as reported by Bloomberg L.P. or, if not reported therein, in another authoritative source mutually selected by MPLX and ANDX) on each of the ten consecutive trading days ending with the complete trading day immediately prior to the effective time of the Merger.

Consideration to ANDX Series A Preferred Unitholders

As a result of the Merger, each ANDX Series A Preferred Unit issued and outstanding immediately prior to the effective time of the Merger will be converted into the right to receive a validly issued, fully paid and non-assessable (except to the extent such non-assessability may be affected by Sections 17-303, 17-607 and 17-804 of the DRULPA) MPLX Series B Preferred Unit. By virtue of the conversion, each ANDX Series A Preferred Unit will be cancelled and cease to exist as of the effective time of the Merger.

Consideration to ANDX TexNew Mex Unitholders and ANDX Special Limited Partner Interest

As a result of the Merger, each ANDX TexNew Mex Unit issued and outstanding immediately prior to the effective time of the Merger will be converted into a validly issued, fully paid and non-assessable (except to the extent such non-assessability may be affected by Sections 17-303, 17-607 and 17-804 of the DRULPA) MPLX

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TexNew Mex Unit representing a limited partner interest in MPLX. By virtue of the conversion, all ANDX TexNew Mex Units will be cancelled and cease to exist as of the effective time of the Merger. The MPLX TexNew Mex Units are a new class of units in MPLX with substantially equivalent rights, powers, duties and obligations as the TexNew Mex Units.

As a result of the Merger, the ANDX Special Limited Partner Interest outstanding immediately prior to the effective time of the Merger will be converted into the MPLX Special Limited Partner Interest and the ANDX Special Limited Partner Interest shall be deemed to be cancelled and shall cease to exist as of the effective time of the Merger.

Background of the Merger

On October 1, 2018, MPC completed its acquisition of Andeavor, pursuant to the Agreement and Plan of Merger, dated as of April 29, 2018 (as amended, the “Andeavor Merger Agreement”), by and among Andeavor, MPC, Mahi Inc., a Delaware corporation and a wholly owned subsidiary of MPC, and Andeavor LLC (f/k/a Mahi LLC), a Delaware limited liability company and a wholly owned subsidiary of MPC. As a result of this transaction and Andeavor becoming a direct wholly owned subsidiary of MPC, MPC obtained the ability to control ANDX through its indirect ownership of the ANDX GP. In addition, as a result of this transaction, MPC acquired beneficial ownership of ANDX Common Units owned at the time by Andeavor and its subsidiaries, representing approximately 64% of the outstanding ANDX Common Units.

In its earnings release issued on November 1, 2018, MPC stated its plans to engage advisors and begin the process of assessing all options for MPLX and ANDX, which could include MPLX acquiring ANDX and ANDX acquiring MPLX.

On November 5, 2018, MPC filed with the SEC amendments to its Schedules 13D relating to both ANDX and MPLX with updated information regarding the assessment of such options.

On November 26, 2018, at the request of Sigmund Cornelius, chairman of the ANDX Conflicts Committee, a representative of Sidley Austin LLP (“Sidley”) contacted representatives of MPC to determine whether Sidley had any potential conflicts that would prevent it from serving as legal advisor to the ANDX Conflicts Committee in connection with the consideration, negotiation and, if appropriate, approval of a potential transaction with MPLX.

On December 3, 2018, the ANDX Conflicts Committee engaged Sidley as its legal advisor in connection with a potential transaction with MPLX. An engagement letter between the ANDX Conflicts Committee and Sidley relating to the same was subsequently executed effective as of such date.

On December 6, 2018, the ANDX Conflicts Committee held separate in-person meetings, also attended by a representative of Sidley, to interview four potential financial advisors. During these interviews, the ANDX Conflicts Committee discussed each financial advisor’s knowledge of precedent simplification and related-party master limited partnership (“MLP”) transactions, experience with conflicts committee assignments (including MLP conflicts committees), prior relationships with MPC, MPLX and ANDX, and proposed fees for its work. Goldman Sachs also delivered to the ANDX Conflicts Committee a relationships disclosure letter. Following the last interview, the ANDX Conflicts Committee held a meeting along with the representative of Sidley, at which meeting the ANDX Conflicts Committee members discussed the interviews, the relative strengths and weaknesses of each of the potential financial advisors, their independence, and their proposed fees. The ANDX Conflicts Committee unanimously agreed to select Goldman Sachs as its financial advisor, subject to negotiation of an acceptable fee and engagement letter with Goldman Sachs. The ANDX Conflicts Committee determined to wait to notify Goldman Sachs until the committee received final information from one of the other prospective financial advisors.

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On December 8, 2018, Goldman Sachs delivered a draft engagement letter to the ANDX Conflicts Committee. The ANDX Conflicts Committee and representatives of Sidley engaged in negotiations with Goldman Sachs regarding the engagement letter until December 27, 2018, on which date Goldman Sachs delivered an executed engagement letter that was subsequently executed by the ANDX Conflicts Committee and ANDX. Under the terms of the engagement letter, Goldman Sachs was not entitled to an initial fee unless and until a proposal relating to a transaction was received by the ANDX Conflicts Committee.

On December 17, 2018, at the request of Christopher Helms, chairman of the conflicts committee of the board of directors of MPLX GP (the “MPLX Conflicts Committee”), representatives of MPC contacted Latham & Watkins LLP (“Latham & Watkins”) to determine whether Latham & Watkins had any potential conflicts that would prevent Latham & Watkins from serving as legal advisor to the MPLX Conflicts Committee in connection with the consideration, negotiation and, if appropriate, approval of a potential transaction with ANDX. On December 19, 2018, Michael Beatty, a member of the MPLX Conflicts Committee, contacted a representative of Latham & Watkins regarding the engagement of Latham & Watkins as legal advisor to the MPLX Conflicts Committee.

Also in December 2018, the MPLX Conflicts Committee contacted Jefferies LLC (“Jefferies”) regarding potential service as financial advisor to the MPLX Conflicts Committee in connection with the consideration, negotiation and, if appropriate, approval of a potential transaction with ANDX.

On January 7, 2019, Mr. Beatty again contacted a representative of Latham & Watkins regarding the engagement of Latham & Watkins as legal advisor to the MPLX Conflicts Committee.

On January 9, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins. During this meeting, representatives of Jefferies and Latham & Watkins provided an overview of their respective qualifications and experience advising MLPs and other companies with respect to transactions similar to the proposed transaction with ANDX. Latham & Watkins also provided an overview of its prior relationships with MPC, MPLX and ANDX. After discussion, the MPLX Conflicts Committee unanimously determined to engage Jefferies and Latham & Watkins as financial advisor and legal counsel, respectively, to the MPLX Conflicts Committee.

On January 17, 2019, Sidley and Latham & Watkins delivered a joint legal due diligence request list to MPC, MPLX and ANDX.

On January 25, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins. During this meeting, Latham & Watkins reviewed with the MPLX Conflicts Committee the responsibilities of the MPLX Conflicts Committee members in connection with their consideration of a potential transaction under Delaware law and pursuant to the MPLX Partnership Agreement, including with respect to resolving conflicts of interests in accordance with the MPLX Partnership Agreement. Jefferies and Latham & Watkins each also reviewed with the MPLX Conflicts Committee the status of their respective due diligence reviews of ANDX to date.

On January 30, 2019, representatives of Sidley and Latham & Watkins held a telephonic meeting with MPC in-house legal representatives to discuss the due diligence request and the parties’ planned due diligence reviews of ANDX and MPLX, including virtual data room requirements and process-related responses.

On February 13, 2019, Sidley delivered a memorandum regarding duties of directors under Delaware law and pursuant to the ANDX Partnership Agreement to the ANDX Conflicts Committee in anticipation of a due diligence session and further meetings.

On February 13, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss upcoming management presentations with representatives of MPC, ANDX and MPLX.

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On February 14, 2019, Latham & Watkins hosted a diligence and management presentation session in Houston, Texas, with representatives of MPC management, ANDX management and MPLX management, including Michael Hennigan, in his capacity as the President of MPLX GP, Pamela Beall, in her capacity as the Executive Vice President and Chief Financial Officer of MPLX GP, Don Sorensen, President of ANDX GP, Andrew Woodward, former Vice President, Finance of ANDX GP, and Timothy Griffith, in his capacity as the Senior Vice President and Chief Financial Officer of MPC; the ANDX Conflicts Committee; the MPLX Conflicts Committee, with Dan Sandman joining by telephone; Goldman Sachs; Barclays plc (“Barclays”), MPC’s financial advisor in connection with strategic alternatives for MPLX and ANDX; Jefferies; Sidley; and Latham & Watkins in attendance. At the management presentation, members of management of each of MPC, ANDX and MPLX discussed with the conflicts committees and their advisors the strategic rationale for a potential transaction as well as current business plans for each of ANDX and MPLX, including certain unaudited forecasted financial information regarding the applicable entities and their respective assets.

Following the management presentations, the ANDX Conflicts Committee members in attendance met with representatives from Goldman Sachs and Sidley to discuss the presentations and related matters, and the MPLX Conflicts Committee met with Mr. Hennigan, in his capacity as the President of MPLX GP, and Ms. Beall, in her capacity as the Executive Vice President and Chief Financial Officer of MPLX GP, to discuss the presentations and related matters, including certain considerations with respect to a potential transaction such as MPLX’s estimates of expected required capital expenditures pertaining to ANDX’s assets based on a report prepared by MPC regarding such capital expenditures (the “MPC CapEx Report”). Mr. Hennigan offered to send the MPC CapEx Report to the MPLX Conflicts Committee for review. Mr. Hennigan and Ms. Beall then left the meeting. Thereafter, the MPLX Conflicts Committee, with Mr. Sandman participating by telephone, held a meeting with representatives of Jefferies and Latham & Watkins to discuss the management presentations and related matters, as well as the overall transaction timeline and due diligence process.

On February 15, 2019, Jefferies delivered to the MPLX Conflicts Committee a relationships disclosure letter.

On February 19, 2019, at a meeting of the board of directors of MPLX GP (the “MPLX Board”), the MPLX Board adopted resolutions delegating to the MPLX Conflicts Committee the full power, authority and responsibilities of the MPLX Board to the extent necessary to (i) develop, in conjunction with the full MPLX Board, a proposal to ANDX regarding a potential transaction or series of related transactions pursuant to which MPLX or one of its affiliates would directly or indirectly acquire all of the outstanding partnership interests of ANDX, (ii) review and evaluate any potential conflicts arising in connection with the proposal and the proposed transaction and related arrangements, (iii) review and evaluate the terms and conditions of the proposal and the proposed transaction and related arrangements on behalf of MPLX and the holders of limited partner interests in MPLX (other than MPLX GP and its affiliates, including MPC) (the “MPLX Public Unitholders”), (iv) negotiate on behalf of MPLX the terms and conditions of the proposed transaction and related arrangements, (v) determine whether the proposed transaction and related arrangements are not adverse to the best interests of MPLX and its subsidiaries treated as a single consolidated entity and the MPLX Public Unitholders, and (vi) determine whether to approve or not approve, and to recommend that the MPLX Board approve or not approve, as applicable, the proposed transaction and related arrangements, with any such approval and related recommendation of the MPLX Conflicts Committee constituting “Special Approval” for all purposes under the MPLX Partnership Agreement, including but not limited to Section 7.9 thereof.

Also at the February 19, 2019 MPLX Board meeting, the MPLX Board reviewed a presentation (the “February 19 Presentation”) containing a summary of proposed terms of a potential acquisition by MPLX of all outstanding ANDX Common Units that had been provided to the MPLX Board by representatives of MPC. The February 19 Presentation outlined a unit-for-unit exchange at an exchange ratio of 1.042 MPLX Common Units for each ANDX Common Unit, including the key assumptions and projections underlying the proposed terms of such acquisition.

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On February 20, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the terms of the proposed transaction contained in the February 19 Presentation, including the key assumptions and projections related thereto. Representatives of Latham & Watkins also reviewed with the MPLX Conflicts Committee the status of Latham & Watkins’ legal due diligence review of ANDX.

On February 25, 2019, Mr. Hennigan sent a copy of the MPC CapEx Report to representatives of Latham & Watkins in response to a follow-up request by representatives of Latham & Watkins.

On February 27, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to further discuss the terms of the proposed transaction contained in the February 19 Presentation. Jefferies reviewed with the MPLX Conflicts Committee its preliminary financial analysis of the terms of the proposed transaction contained in the February 19 Presentation and provided an overview of comparable precedent transactions.

On March 1, 2019, the MPLX Conflicts Committee held a telephonic meeting (the “March 1 Meeting”) with Mr. Hennigan and Ms. Beall to discuss considerations related to a potential merger transaction between MPLX and ANDX. At the March 1 Meeting, Mr. Hennigan and Ms. Beall discussed with the MPLX Conflicts Committee certain of Mr. Hennigan’s and Ms. Beall’s observations regarding the valuation of ANDX and the potential terms of the transaction as outlined in the February 19 Presentation.

Later that day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to further discuss the March 1 Meeting. Representatives of Jefferies discussed Jefferies’ preliminary analysis of the proposed transaction. Representatives of Jefferies, among other things, (i) summarized the transaction and provided background on each of MPLX and ANDX and their respective businesses, (ii) reviewed the proposed exchange ratio of 1.042 contained in the February 19 Presentation in the context of an implied multiples analysis, (iii) discussed summary market data for the MPLX Common Units and the ANDX Common Units, along with implied multiples with respect thereto relating to, among other things, total equity value, EBITDA and distributable cash flow, and (iv) described the implied premiums to pricing sensitivity analysis undertaken by Jefferies. The MPLX Conflicts Committee then discussed with representatives of Jefferies and Latham & Watkins the strategic considerations involved in providing an initial proposal to ANDX with respect to a potential transaction, as well as the overall transaction negotiations and execution process. Jefferies and Latham & Watkins also provided updates with respect to their respective due diligence reviews of ANDX.

On March 13, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins. Representatives of Jefferies further discussed Jefferies’ preliminary analysis of the proposed transaction. The MPLX Conflicts Committee then discussed with representatives of Jefferies and Latham & Watkins additional strategic considerations involved in providing an initial proposal to ANDX with respect to a potential transaction. Jefferies and Latham & Watkins also provided updates with respect to their respective due diligence reviews of ANDX. Following the meeting, at the direction of the MPLX Conflicts Committee, Latham & Watkins provided a draft of an initial offer letter proposing a unit-for-unit exchange at an exchange ratio of 1.02 MPLX Common Units for each ANDX Common Unit for the MPLX Conflicts Committee’s review.

On March 14, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to review the draft offer letter and other economic and strategic considerations related to making an initial offer. Following this discussion, the MPLX Conflicts Committee unanimously determined to send the offer letter the following day to the ANDX Conflicts Committee, including a proposed exchange ratio for the potential merger transaction of 1.02 MPLX Common Units for each ANDX Common Unit.

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On March 15, 2019, Mr. Helms, as chairman of the MPLX Conflicts Committee, delivered to Gary Heminger, in his capacity as the chairman and chief executive officer of ANDX GP, a letter dated March 15, 2019 (the “March 15 Letter”) and addressed to the ANDX Conflicts Committee containing the MPLX Conflicts Committee’s proposal for a strategic transaction between MPLX and ANDX. The proposal provided for the acquisition of ANDX by MPLX at an exchange ratio of 1.02 MPLX Common Units for each outstanding ANDX Common Unit (the “Initial MPLX Offer”). The March 15 Letter further noted that the MPLX Conflicts Committee would appreciate an opportunity to present its proposal in more detail to the ANDX Conflicts Committee and its advisors as soon as possible.

On March 18, 2019, Mr. Heminger forwarded the March 15 Letter to the ANDX Board, along with a letter dated March 18, 2019, from Mr. Heminger, in his capacity as chairman and chief executive officer of the ANDX Board, to Mr. Cornelius as chairman of the ANDX Conflicts Committee. In his letter, Mr. Heminger requested that the ANDX Conflicts Committee proceed with a review and evaluation of the Initial MPLX Offer pursuant to Section 7.9 of the ANDX Partnership Agreement (i.e., as a “Special Approval”), with an understanding that the ANDX Board would ultimately make any determination whether to approve or not approve any combination of ANDX and MPLX. Mr. Heminger further noted in the letter that the ANDX Board had previously authorized the ANDX Conflicts Committee to engage Goldman Sachs and Sidley as its financial and legal advisors, respectively, and that it was the intention of the ANDX Board for the ANDX Conflicts Committee to engage with the MPLX Conflicts Committee in an evaluation of a possible combination of the two partnerships.

On March 19, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. The representatives of Goldman Sachs provided an overview of the Initial MPLX Offer and discussed certain financial aspects of the Initial MPLX Offer with the ANDX Conflicts Committee. The ANDX Conflicts Committee discussed the Initial MPLX Offer and further process matters in connection with the same.

Also on March 19, 2019, representatives of Jefferies contacted representatives of Goldman Sachs and offered to meet in order to discuss the MPLX Conflicts Committee’s reasons for the exchange ratio proposed in the Initial MPLX Offer. Representatives of Goldman Sachs indicated that Goldman Sachs would respond to Jefferies’ request at a future time.

On March 21, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the transaction and steps to be taken while awaiting ANDX’s response to the Initial MPLX Offer. Representatives of Jefferies described Jefferies’ March 19 discussion with Goldman Sachs. Jefferies and Latham & Watkins also provided updates with respect to their respective due diligence reviews of ANDX.

On March 27, 2019, Jones Day, counsel to MPC, provided Latham & Watkins with an initial draft of the Merger Agreement and proposed transaction timeline.

On April 1, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins. Representatives of Latham & Watkins reviewed with the MPLX Conflicts Committee the terms of the initial draft Merger Agreement that Jones Day had provided to Latham & Watkins. The MPLX Conflicts Committee determined that, while the committee had not received a response from the ANDX Conflicts Committee to the Initial MPLX Offer, the committee and Latham & Watkins should provide comments to the Merger Agreement in order to be constructive and make progress on the transaction. Representatives of Latham & Watkins also reviewed with the MPLX Conflicts Committee the status of Latham & Watkins’ legal due diligence review of ANDX and the proposed timeline provided by Jones Day.

On April 2, 2019, the ANDX Conflicts Committee held a meeting in person at the offices of Goldman Sachs, with James Lamanna joining by telephone, along with representatives of Goldman Sachs and Sidley. At the meeting, representatives of Goldman Sachs discussed with the ANDX Conflicts Committee Goldman Sachs’

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preliminary financial analysis of the financial terms of the Initial MPLX Offer. The ANDX Conflicts Committee then discussed the Initial MPLX Offer and strategies it might pursue with respect to next steps. Based on the ANDX Conflicts Committee’s evaluation of the Initial MPLX Offer, and after consultation with representatives of Goldman Sachs and Sidley, the ANDX Conflicts Committee determined to reject the Initial MPLX Offer, and further concluded that the Initial MPLX Offer did not serve as a basis for any further negotiation (the “Initial ANDX Response”).

Also on April 2, 2019, at the direction of the MPLX Conflicts Committee, Latham & Watkins provided Jones Day with a revised draft of the Merger Agreement, including revisions to, among other things, certain representations, warranties, interim covenants and termination rights of the parties.

On that same day, the ANDX Board adopted a resolution by written consent delegating to the ANDX Conflicts Committee, the power and authority to: (i) review and evaluate the terms and conditions of, and to determine the advisability of, the Initial MPLX Offer and any alternative transaction thereto with MPLX on behalf of ANDX and the ANDX Common Unitholders excluding ANDX GP and ANDX Refining Southwest (the “ANDX Public Unitholders”); (ii) negotiate, or delegate to any person or persons the ability to negotiate, with MPLX and its representatives, or any other appropriate person, with respect to the terms and conditions of the Proposed Transaction (including any ancillary agreements with MPC); (iii) determine whether or not to approve the Proposed Transaction by “Special Approval” (pursuant to Section 7.9(a) of the ANDX Partnership Agreement); and (iv) make any recommendations to the ANDX Board regarding the proposed transaction as the ANDX Conflicts Committee shall determine to be appropriate.

On April 3, 2019, Mr. Cornelius, acting on behalf of the ANDX Conflicts Committee, delivered a letter (the “April 3 Letter”) to Mr. Helms stating the Initial ANDX Response. The April 3 Letter further indicated that the ANDX Conflicts Committee would be willing to review, evaluate and potentially negotiate a revised proposal by the MPLX Conflicts Committee, but that the ANDX Conflicts Committee did not believe a presentation by the MPLX Conflicts Committee and its advisors regarding the Initial MPLX Offer would be productive at that time.

Later that day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the April 3 Letter and a potential response thereto. Following this discussion, the MPLX Conflicts Committee decided to advise MPC that, based on the April 3 Letter, it appeared that discussions with ANDX may have reached an impasse and that the MPLX Conflicts Committee would not negotiate against itself by submitting a revised offer to the ANDX Conflicts Committee. Representatives of Latham & Watkins then reviewed with the MPLX Conflicts Committee additional revisions to the Merger Agreement, including revisions to limit ANDX’s ability to amend existing related-party agreements with MPC after the signing of the Merger Agreement. Following the meeting, at the direction of the MPLX Conflicts Committee, Latham & Watkins provided Jones Day with a further revised draft of the Merger Agreement containing the revisions discussed with the MPLX Conflicts Committee.

On April 5, 2019, representatives of Barclays, at the direction of MPC, contacted representatives of Jefferies and asked Jefferies to contact Goldman Sachs in order to obtain an understanding of why the ANDX Conflicts Committee concluded that the Initial MPLX Offer did not serve as a basis for further negotiation.

Later that same day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss Barclays’ request for Jefferies to contact Goldman Sachs. Following discussion, the MPLX Conflicts Committee authorized Jefferies to contact Goldman Sachs and offer to discuss the MPLX Conflicts Committee’s reasons for the exchange ratio reflected in the Initial MPLX Offer.

On April 7, 2019, representatives of Jefferies spoke by phone with representatives of Goldman Sachs and explained to Goldman Sachs that the MPLX Conflicts Committee did not plan to provide a revised offer.

Later that same day, representatives of Jefferies contacted representatives of Goldman Sachs in order to discuss the Initial MPLX Offer and the Initial ANDX Response. Goldman Sachs responded that the ANDX

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Conflicts Committee did not view the Initial MPLX Offer as a valid starting point for discussions and that the ANDX Conflicts Committee had determined not to pursue a potential transaction on those terms. Representatives of Jefferies subsequently contacted representatives of Barclays and relayed the substance of Jefferies’ discussions with Goldman Sachs.

On April 8, 2019, Mr. Heminger, acting on behalf of MPC, spoke by phone with Mr. Cornelius. Mr. Heminger explained that he was looking for a way to advance the discussions and encouraged the ANDX Conflicts Committee to make a proposal. Mr. Cornelius informed Mr. Heminger that the ANDX Conflicts Committee was scheduled to meet on April 10, 2019 and that he would reach out to Mr. Heminger after the meeting.

Also on April 8, 2019, representatives of Barclays, at the direction of MPC, contacted representatives of Jefferies and Goldman Sachs and proposed that the parties’ respective financial advisors meet in person the following week.

Later that same day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss Jefferies’ conversations with Goldman Sachs and Barclays, as well as the merits of the proposed meeting of the parties’ financial advisors. Following discussion, the MPLX Conflicts Committee authorized Jefferies to participate in the meeting and share with Barclays and Goldman Sachs certain aspects of Jefferies’ financial analysis of the proposed business combination.

On April 9, 2019, representatives of MPC held a telephonic conversation with representatives of Latham & Watkins during which Latham & Watkins discussed with such representatives the general status of negotiations among the parties.

On April 10, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley to discuss whether or not to make a counterproposal to the Initial MPLX Offer. Representatives of Goldman Sachs updated the ANDX Conflicts Committee on its previous discussions with representatives of Jefferies regarding the Initial ANDX Response. Mr. Cornelius advised the ANDX Conflicts Committee on his discussions with Mr. Heminger, explaining that Mr. Heminger had expressed his hope that the parties could advance negotiations even in light of the Initial ANDX Response. The ANDX Conflicts Committee engaged in discussions with Goldman Sachs and Sidley regarding whether or not to make a counterproposal and requested that Goldman Sachs reach out to Jefferies and Barclays to attempt to break through the impasse.

Later on April 10, 2019, Mr. Cornelius spoke with Mr. Heminger. Mr. Cornelius stated the ANDX Conflicts Committee agreed with MPC’s proposal for representatives of Goldman Sachs, Jefferies and Barclays to meet.

On April 11, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the proposed meeting of the parties’ financial advisors. Representatives of Jefferies reviewed with the MPLX Conflicts Committee certain information that Jefferies intended to share with Barclays and Goldman Sachs. Latham & Watkins then provided the MPLX Conflicts Committee with a description of Latham & Watkins’ April 9 telephonic conversation with representatives of MPC.

On April 15, 2019, representatives of Goldman Sachs, Jefferies and Barclays met in New York City and discussed the assumptions being utilized by Goldman Sachs and Jefferies for their respective financial analyses. The representatives of Goldman Sachs, Jefferies and Barclays also discussed the financial impact of those assumptions on their respective financial analyses of illustrative exchange ratios for a potential transaction.

Later that same day, representatives of Jefferies held a telephonic conversation with Mr. Heminger acting on behalf of MPC, and Mr. Hennigan, acting on behalf of MPLX GP, in which Jefferies discussed the general status of negotiations among the parties and suggested that either the ANDX Conflicts Committee propose a counteroffer or that MPC make an alternative proposal to both committees.

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On April 16, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. At the meeting, representatives of Goldman Sachs provided an update on their discussions with representatives of Barclays and Jefferies, including a summary of the perspectives of Jefferies and MPLX management as to the future financial performance of the companies, and Jefferies’ representation that the MPLX Conflicts Committee would not be making another offer. The ANDX Conflicts Committee discussed next steps in developing a potential counteroffer, and requested that Goldman Sachs provide further analysis on potential exchange ratios.

Later that same day, Mr. Heminger contacted Mr. Cornelius to schedule a call. Mr. Cornelius informed Mr. Heminger that the ANDX Conflicts Committee had received a debrief from the three financial advisors’ meeting and that the ANDX Conflicts Committee was developing a counteroffer.

On April 17, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins at which representatives of Jefferies provided a summary of the meeting of the parties’ respective financial advisors held on April 15, 2019. The MPLX Conflicts Committee discussed whether to propose that MPC offer some form of sponsor support in order to resolve the potential impasse between the parties.

Later that same day, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley to continue discussing a potential counteroffer. Representatives of Goldman Sachs discussed the ANDX and MPLX management forecasts and ANDX and MPLX street estimates, the estimates and forecasts of securities analysts covering ANDX and MPLX, as well as an updated preliminary financial analysis of a potential transaction. At that meeting, the ANDX Conflicts Committee authorized Mr. Cornelius to make a counteroffer of 1.35 MPLX Common Units for each outstanding ANDX Common Unit (the “Second ANDX Response”). Thereafter, Mr. Cornelius delivered a letter setting forth the Second ANDX Response to Mr. Helms.

On April 18, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the Second ANDX Response. Representatives of Jefferies discussed Jefferies’ analysis of the proposed exchange ratio in the Second ANDX Response. The MPLX Conflicts Committee discussed with representatives of Jefferies and Latham & Watkins whether to respond to the Second ANDX Response. Following discussion, the MPLX Conflicts Committee decided to consider responding to the Second ANDX Response with an increased exchange ratio, and Latham & Watkins provided a draft counteroffer letter to the MPLX Conflicts Committee for review.

Also on April 18, 2019, at the direction of the MPLX Conflicts Committee, representatives of Jefferies discussed the transaction and the MPLX Conflicts Committee’s proposed counteroffer with representatives of Barclays, and Barclays, on behalf of MPC, requested that the MPLX Conflicts Committee refrain from sending the counteroffer letter to ANDX until Mr. Heminger spoke to Mr. Cornelius.

Later that same day, Mr. Heminger, acting on behalf of MPC, and Mr. Cornelius spoke by phone. Mr. Heminger thanked Mr. Cornelius for sending the Second ANDX Response, but also expressed his concern with its content and asked for the ANDX Conflicts Committee’s rationale for its offer. Mr. Cornelius stated that the Initial MPLX Offer was substantially below market, was inconsistent with precedent transactions, ignored the historical valuation relationship between the entities and did not represent a constructive starting point for negotiations. However, in the interest of finding a path forward, Mr. Cornelius noted that the ANDX Conflicts Committee was willing to communicate the Second ANDX Response. Mr. Cornelius noted such proposal was supported by longer-term historical related values between the two securities, and that it would enable the pro forma company to pay the current MPLX distribution while maintaining an approximate 1.4x coverage ratio. Mr. Cornelius also cited the ANDX Conflicts Committee’s belief that the proposed transaction would be slightly accretive to ANDX and roughly breakeven for MPLX and MPC. Mr. Heminger stated his view that the proposal would represent a dilutive transaction to MPLX on a DCF-per-unit basis.

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Mr. Cornelius suggested that the financial advisors speak again to understand differences in calculations, and they agreed that Mr. Heminger, acting on behalf of MPC, should request that Barclays and Jefferies contact Goldman Sachs to discuss this further.

Also later that day, representatives of Barclays, Jefferies and Goldman Sachs held a telephonic meeting to further discuss the respective financial analysis methodologies of each financial advisor.

On April 19, 2019, Mr. Heminger, acting on behalf of MPC, and Mr. Cornelius corresponded regarding the different analytical approaches being discussed and used by the respective financial advisors to the ANDX Conflicts Committee and the MPLX Conflicts Committee and by Barclays, as financial advisor to MPC, including analysis regarding “distributable cash flow” and “discounted cash flow” metrics and their prior discussions regarding the “dueling DCFs” in certain earlier communications, along with assumptions being used in the financial analyses to assess the financial impact of illustrative exchange ratios for a potential transaction.

On April 20, 2019, Mr. Heminger, acting on behalf of MPC, and Mr. Cornelius spoke again by phone. Mr. Heminger agreed to look at comparisons based on management forecasts, with no adjustments, and for MPC to work on an offer to the ANDX Conflicts Committee in support of the transaction, noting his understanding that MPC support in the form of a different exchange ratio would likely be required to get a deal done. Mr. Heminger also noted that MPC considered the accretion/dilution to remain much more favorable to ANDX in 2019 and later years, and stated that he could not support a transaction even at a 1.15x exchange ratio, particularly due to the DCF-per-unit dilution for MPLX in years 2020 and beyond. Mr. Cornelius said he would wait for MPLX’s next offer and respond accordingly.

Also on April 20, 2019, Mr. Heminger, acting on behalf of MPC, contacted Mr. Helms and discussed the transaction, including the financial analysis methodologies discussed between MPC and Barclays. Mr. Heminger informed Mr. Helms of his belief that an exchange ratio of 1.06 MPLX Common Units for each outstanding ANDX Common Unit could be sufficient to reach an agreement among the parties.

Later that same day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the proposed counteroffer letter drafted by Latham & Watkins. Representatives of Jefferies provided the MPLX Conflicts Committee with a description of its April 18 conversations with Barclays and Goldman Sachs, and Mr. Helms provided the committee with a description of his earlier conversation with Mr. Heminger, including Mr. Heminger’s belief that a 1.06x exchange ratio could be sufficient to reach an agreement on the transaction. Jefferies provided the committee with its analysis of a proposed exchange ratio of 1.06 MPLX Common Units for each outstanding ANDX Common Unit. Following discussion, the MPLX Conflicts Committee determined to respond to the Second ANDX Response by sending the ANDX Conflicts Committee the counteroffer letter proposing an all-unit transaction with an exchange ratio of 1.06 MPLX Common Units for each outstanding ANDX Common Unit, representing a 1.7% premium based on the closing prices of the ANDX Common Units and the MPLX Common Units on April 18, 2019 (the “Second MPLX Offer”). The MPLX Conflicts Committee also discussed that MPC could offer some form of subsidy in order to support a higher exchange ratio to the ANDX Public Unitholders by agreeing to receive a lower exchange ratio for ANDX Common Units held by affiliates of MPC. Later that same day, Mr. Helms, on behalf of the MPLX Conflicts Committee, delivered the Second MPLX Offer to Mr. Cornelius.

On April 22, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. Representatives of Goldman Sachs discussed with the committee members preliminary financial analyses of the Second MPLX Offer. After discussion, the ANDX Conflicts Committee approved sending a counteroffer with an exchange ratio of 1.30 MPLX Common Units for each outstanding ANDX Common Unit (the “Third ANDX Response”). Later that same day, Mr. Cornelius, on behalf of the ANDX Conflicts Committee, delivered the Third ANDX Response to Mr. Helms.

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Also on April 22, 2019, Mr. Heminger, acting on behalf of MPC, spoke by phone with Mr. Cornelius. Mr. Heminger stated that he wanted to understand the logic for the Third ANDX Response, believing that it was dilutive on a DCF-per-unit basis to MPLX. Mr. Cornelius stated that the Second MPLX Offer was dilutive to ANDX and represented a below-market transaction. Additionally, Mr. Cornelius explained the ANDX Conflicts Committee believed that the ANDX Common Unit price reflected ANDX management’s public commentary regarding its financial policies. Mr. Cornelius highlighted that the ANDX Conflicts Committee believed the Second MPLX Offer fell short on a number of metrics important in the evaluation of a transaction, including: (i) the Second MPLX Offer would be value dilutive to ANDX using a discounted cash flow valuation and dilutive based on a distributable cash flow analysis; (ii) management’s forecasts for MPLX were substantially more bullish than analyst estimates and, based on analyst estimates for both ANDX and MPLX, the Second MPLX Offer was even more value destructive and dilutive to ANDX; and (iii) as the Second MPLX Offer represented an at or below market offer, the premium implied by the Second MPLX Offer would be among the lowest in precedent transactions.

Later that same day, Mr. Heminger and Mr. Cornelius spoke again by phone. Mr. Heminger, acting on behalf of MPC, proposed a merger transaction in which the ANDX Public Unitholders would receive 1.10 MPLX Common Units for each of their ANDX Common Units, while MPC’s affiliates would receive an “at market” exchange ratio for the ANDX Common Units held by such affiliates (the “Initial MPC Proposal”). Mr. Heminger noted that the Initial MPC Proposal would provide a premium to the ANDX Public Unitholders and be marginally accretive to both ANDX and MPLX, and stated that he did not contemplate MPC providing any additional financial support to facilitate a transaction. Mr. Cornelius noted that he would communicate the Initial MPC Proposal to the ANDX Conflicts Committee.

On April 23, 2019, the ANDX Board held a regularly scheduled meeting in Findlay, Ohio. Discussion of approval for the regular quarterly distribution by ANDX was tabled at that time.

On April 24, 2019, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the Third ANDX Response. In light of the exchange ratio proposed by the ANDX Conflicts Committee in the Third ANDX Response, the MPLX Conflicts Committee discussed with representatives of Jefferies and Latham & Watkins possible alternative transactions for the acquisition of ANDX by MPLX. The MPLX Conflicts Committee directed Latham & Watkins to discuss potential alternative transactions with representatives of MPC and MPLX and to report back to the MPLX Conflicts Committee.

Also on April 24, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. Representatives of Goldman Sachs discussed preliminary financial analyses of the Initial MPC Proposal. After discussions with representatives of Goldman Sachs and Sidley, the ANDX Conflicts Committee authorized Mr. Cornelius to make a counteroffer to MPC with a 1.20x exchange ratio for the ANDX Public Unitholders and a 1.04x exchange ratio for the ANDX Common Units held by MPC’s affiliates (the “April 24 ANDX Response”).

Later that same day, Mr. Cornelius and Mr. Heminger, acting on behalf of MPC, spoke by phone, with Mr. Griffith in the room with Mr. Heminger. Mr. Cornelius presented the April 24 ANDX Response to Mr. Heminger. Mr. Heminger expressed his disappointment with the counteroffer. Mr. Heminger reiterated that he did not contemplate MPC providing any additional financial support to facilitate a transaction. Mr. Cornelius reviewed various talking points several times regarding the items that he had discussed with Mr. Heminger on April 22, 2019 in connection with the Third ANDX Response. Mr. Heminger stated that he was going to advise the MPC board of directors (the “MPC Board”) and the MPLX GP Board of the April 24 ANDX Response.

Later that same day, the MPLX Conflicts Committee met with Mr. Heminger, Mr. Griffith and other representatives of MPC to discuss the exchange ratio proposed by the ANDX Conflicts Committee in the Third ANDX Response. Mr. Heminger asked whether the MPLX Conflicts Committee would be willing to offer up to 1.07 MPLX Common Units for each outstanding ANDX Common Unit in support of a potential merger

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transaction with ANDX. After meeting privately to discuss Mr. Heminger’s inquiry, the MPLX Conflicts Committee indicated to Mr. Heminger that the MPLX Conflicts Committee would be willing to offer up to 1.07 MPLX Common Units for each outstanding ANDX Common Unit in support of a potential merger transaction with ANDX, but that the MPLX Conflicts Committee would not support an exchange ratio higher than 1.07 MPLX Common Units for each outstanding ANDX Common Unit.

Later that same day, the MPLX Board held a regularly scheduled meeting in Findlay, Ohio.

On the morning of April 25, 2019, Mr. Cornelius spoke with Mr. Heminger. Mr. Heminger, acting on behalf of MPC, stated he wanted to be responsive to the ANDX Conflicts Committee’s concerns about the dilutive impact of the Initial MPC Proposal to the ANDX Public Unitholders. To help bridge the differences between the Initial MPC Proposal and the April 24 ANDX Response, Mr. Heminger, acting on behalf of MPC, proposed that MPC would make a supplemental cash payment to the ANDX Public Unitholders in order to make the Initial MPC Proposal 2.5% accretive to ANDX Public Unitholders for 2019.

Later that same morning, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. Mr. Cornelius provided the ANDX Conflicts Committee an overview of his conversation with Mr. Heminger prior to the meeting and the proposed supplemental cash payment. The ANDX Conflicts Committee requested Goldman Sachs provide an updated analysis of the Initial MPC Proposal, including the supplemental cash payment. The ANDX Conflicts Committee adjourned the meeting to be reconvened later that day.

Following the ANDX Conflicts Committee meeting, Mr. Cornelius emailed Mr. Heminger to request a clarification about the dollar amount proposed as a supplemental cash payment. Mr. Heminger responded by email that the amount of parent support, which could include cash to provide 2019 accretion for ANDX Public Unitholders, using MPC management projections, was “in the ballpark of $250 million.”

Later that same day, the ANDX Conflicts Committee reconvened its telephonic meeting with representatives from Goldman Sachs and Sidley. Representatives of Goldman Sachs provided an overview of Goldman Sachs’ and Barclays’ previous discussions regarding certain financial aspects of a potential transaction and different perspectives as to the financial implications of a potential transaction. Additionally, representatives of Goldman Sachs discussed financial analyses of the Initial MPC Proposal, as supplemented by the cash payment proposal. After discussion, the ANDX Conflicts Committee authorized Mr. Cornelius to deliver a counteroffer to Mr. Heminger of (i) a 1.10x exchange ratio for ANDX Public Unitholders, plus cash consideration of $2.75 for each ANDX Common Unit held by the public (representing a total implied cash value of approximately $250 million), noting that this counteroffer represented a value equivalent to a 1.185x exchange ratio, which was less than the April 24 ANDX Response; (ii) with respect to ANDX Common Units held by MPC affiliates, such MPC affiliates would receive an “at-market” exchange ratio and no cash consideration; (iii) a commitment that the quarterly distribution on the ANDX Common Units would be paid at current levels through the closing of the proposed transaction; and (iv) acceptable other terms and conditions around transaction documentation (the “April 25 ANDX Response”). Following the ANDX Conflicts Committee meeting, Mr. Cornelius responded by email to Mr. Heminger with the April 25 ANDX Response.

Later that same day, Mr. Heminger responded by email that his proposal was intended to be inclusive of all value that MPC was forgoing to “top up” the difference between an “at-market” transaction and the value that he believed MPLX would agree to, and then added value to get ANDX Public Unitholders some accretion in 2019. He expressed surprise that the ANDX Conflicts Committee would view his proposal as an additional $250 million in cash. Mr. Heminger stated that his all-in offer represented an exchange ratio of 1.10x to ANDX and a supplemental cash payment in order to have ANDX accretion equal MPLX accretion in the first year (the “April 25 MPC Proposal”).

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On the morning of April 26, 2019, Mr. Cornelius spoke with Mr. Heminger by phone. Mr. Heminger, acting on behalf of MPC, reiterated that he believed the April 25 MPC Proposal was fair. Mr. Cornelius informed Mr. Heminger that the ANDX Conflicts Committee was meeting later that morning.

Later that same morning, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. Representatives of Goldman Sachs discussed preliminary financial analyses of the April 25 MPC Proposal. The ANDX Conflicts Committee requested that Goldman Sachs clarify certain understandings with Barclays before the ANDX Conflicts Committee would send any response to the proposal.

Later that same day, representatives of Goldman Sachs discussed with representatives of Barclays the ANDX Conflicts Committee’s understandings with respect to the April 25 MPC Proposal. Representatives of Barclays provided representatives of Goldman Sachs with additional detail into the basis for the April 25 MPC Proposal; however, representatives of Barclays stated that it was unable to fully explain any discrepancies between Mr. Heminger’s proposal and Mr. Cornelius’ interpretation of the proposal, as representatives of Barclays did not participate in the discussion.

Later that same day, following Mr. Cornelius’ receipt of feedback from representatives of Goldman Sachs regarding their discussions with representatives of Barclays, Mr. Cornelius delivered an email to Mr. Heminger to request in writing the specifics of the April 25 MPC Proposal, including the exchange ratio to be received by the ANDX Public Unitholders, the exchange ratio to be received by MPC’s affiliates, and any cash consideration to be received by the ANDX Public Unitholders. The email noted that the ANDX Conflicts Committee rejected the 1.10x exchange ratio included in the April 25 MPC Proposal, and summarized the follow-up conversations between Mr. Heminger and Mr. Cornelius regarding the inclusion of cash consideration to facilitate a transaction.

Later that same day, Mr. Heminger, acting on behalf of MPC, delivered to Mr. Cornelius via email a written offer proposing an exchange ratio to ANDX Public Unitholders of 1.10x, an exchange ratio to MPC’s affiliates of 1.0528x, and additional discussion to be held regarding any dilution to ANDX Public Unitholders estimated for 2019, with MPC total support not to exceed $250 million in premium forgone on ANDX Common Units held by MPC’s affiliates, together with any contemplated cash consideration (the “April 26 MPC Proposal”).

On the morning of April 27, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. At the meeting, Goldman Sachs discussed preliminary financial analyses of the April 26 MPC Proposal. After discussion, the ANDX Conflicts Committee authorized the delivery of a counteroffer to Mr. Heminger proposing a 1.15x exchange ratio to the ANDX Public Unitholders, with up to 0.05x being payable either in MPLX units or fulfilled in cash of equivalent value (the “April 27 ANDX Response”).

Later that morning, at the direction of MPC and the MPLX Conflicts Committee, Latham & Watkins delivered an initial draft of the Merger Agreement to representatives of Sidley. The initial draft Merger Agreement contemplated, among other things, only a single exchange ratio for all ANDX Common Unitholders, no covenant regarding future levels of ANDX distributions, a support agreement from MPC’s affiliates, and a continuation of waived distributions by MPC’s affiliates on the ANDX Special Limited Partner Interest in a new MPLX Special Limited Partner Interest.

Later that same day, Mr. Cornelius delivered an email counterproposal to Mr. Heminger with the April 27 ANDX Response. The email counterproposal with the April 27 ANDX Response proposed a 1.15x exchange ratio to the ANDX Public Unitholders, noting that the ANDX Conflicts Committee would be receptive to all-equity consideration or a 1.10x exchange ratio for the ANDX Public Unitholders, with the remaining 0.05x exchange ratio fulfilled in cash, which would represent $1.63 per ANDX Common Unit. The email correspondence also noted that the ANDX Conflicts Committee would like a commitment from MPC for the ANDX quarterly distribution to be paid for both the first and second quarters of 2019, as applicable.

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Later that same day, Mr. Cornelius held a call with Mr. Heminger during which Mr. Heminger, acting on behalf of MPC, presented a counteroffer proposing an exchange ratio of 1.11x for the ANDX Public Unitholders, an exchange ratio of 1.0471x for MPC’s affiliates, and MPC’s agreement to hold the ANDX distribution at the proposed first quarter 2019 level for distributions paid in respect of the second and third quarters of 2019 (the “April 27 MPC Proposal”). Mr. Cornelius reiterated the ANDX Conflicts Committee’s position regarding the 1.15x exchange ratio for the ANDX Public Unitholders, but advised Mr. Heminger that he would discuss MPC’s proposal with the full ANDX Conflicts Committee.

Later that evening, the ANDX Conflicts Committee held another teleconference meeting with representatives of Goldman Sachs and Sidley. At the meeting, Goldman Sachs discussed preliminary financial analyses of the April 27 MPC Proposal. Following the meeting, Mr. Cornelius communicated a non-binding counteroffer to Mr. Heminger by email proposing a 1.15x exchange ratio for the ANDX Public Unitholders and a 1.0471x exchange ratio for MPC’s affiliates, and with ANDX distributions to be maintained at current levels through the closing of the proposed transaction. Mr. Cornelius emphasized that the counteroffer “is simply our bottom line.” Mr. Cornelius further noted that such counteroffer would not include any other special voting by ANDX unitholders, such as a “majority of the minority” construct, which is an alternative approval process available to ANDX GP under the ANDX Partnership Agreement in lieu of seeking “Special Approval” from the ANDX Conflicts Committee.

On April 28, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. At this meeting, Goldman Sachs discussed preliminary financial analyses of certain financial aspects of the potential transaction. After further discussion, the ANDX Conflicts Committee members unanimously agreed that the committee’s prior offer proposing a 1.15x exchange ratio for the ANDX Public Unitholders should not be changed, and that Mr. Cornelius should communicate the same to Mr. Heminger.

Later that same day, Mr. Cornelius emailed Mr. Heminger informing him of the ANDX Conflicts Committee’s understanding with respect to the effects of the exchange ratios, and that Mr. Cornelius believed that the ANDX Conflicts Committee remained focused on obtaining the right value for the ANDX Public Unitholders. Mr. Cornelius emphasized that the committee believed the proposed 1.15x exchange ratio for the ANDX Public Unitholders (and the proposed 1.0471x exchange ratio for MPC’s affiliates) should work for all parties, as the committee believed it would be accretive to both ANDX and MPLX, in line with premiums for precedent transactions and represent a value per unit on a discounted cash flow basis only slightly above the status quo valuation based on ANDX management’s forecasts. Mr. Cornelius noted that he expected to receive a call from Mr. Heminger that evening.

Later that evening, Mr. Cornelius and Mr. Heminger spoke again. Mr. Heminger informed Mr. Cornelius that the MPC Board had not authorized him to increase his previous offer regarding sponsor support for the transaction, and informed Mr. Cornelius that he did not believe MPLX would approve a transaction above a 1.07x blended exchange ratio. He asked Mr. Cornelius again whether he could move from the proposed 1.15x exchange ratio, and Mr. Cornelius informed him that the ANDX Conflicts Committee was not able to move under the current facts and circumstances. Mr. Cornelius advised the other ANDX Conflicts Committee members of the conversation.

On April 29, 2019, the ANDX Board held a telephonic meeting at which a regular quarterly distribution for the first quarter of 2019 of $1.03 per ANDX Common Unit was approved. Separately, Mr. Cornelius requested that a meeting of the ANDX Conflicts Committee and its advisors be scheduled for later in the week in anticipation of further discussions.

On May 1, 2019, the ANDX Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Sidley. At the meeting, representatives of Goldman Sachs discussed preliminary financial analyses of certain financial aspects of the potential transaction. After discussion, the ANDX Conflicts Committee determined to wait to hear from MPC or MPLX on any further responses. Mr. Cornelius advised the

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committee members that he would keep them informed on further feedback from Mr. Heminger. He also advised the ANDX Conflicts Committee that he had heard from Gregory Goff, a director of MPLX and ANDX, as well as the Executive Vice Chairman of MPC.

On May 1, 2019, Jones Day sent a draft of the Support Agreement to Latham & Watkins.

On May 2, 2019, Mr. Goff, acting on behalf of MPC, met with Mr. Cornelius at Mr. Cornelius’ office in Houston, Texas. Mr. Goff discussed his understanding of the status of negotiations, his hope that negotiations could advance to conclusion and his views on the risks of a standalone approach for ANDX. Mr. Goff reviewed the Barclays accretion/dilution analysis with Mr. Cornelius, and inquired why prior offers by Mr. Heminger had not been acceptable. Mr. Cornelius responded by pointing to the 1.15x exchange ratio, and asked why that was not acceptable. Mr. Goff then asked whether a 1.135x exchange ratio would work. Mr. Cornelius informed him that he would inquire about that with the ANDX Conflicts Committee.

Later that same day, Mr. Heminger, acting on behalf of MPC, discussed with Mr. Helms a potential merger transaction in which the ANDX Public Unitholders would receive 1.135 MPLX Common Units for each outstanding ANDX Common Unit held by them and MPC’s affiliates would receive 1.0328 MPLX Common Units for each outstanding ANDX Common Unit held by such MPC affiliates, resulting in a blended exchange ratio of 1.07 MPLX Common Units for each outstanding ANDX Common Unit.

Later that evening, Mr. Cornelius and Mr. Heminger spoke by phone. Mr. Heminger, acting on behalf of MPC, confirmed MPC would be interested in pursuing a transaction at a 1.135x exchange ratio for the ANDX Public Unitholders (the “May 2 MPC Proposal”), and Mr. Cornelius informed him that he would inquire with the ANDX Conflicts Committee. Mr. Heminger noted he could not yet confirm a definitive exchange ratio for MPC’s affiliates, as he would need to confirm the calculation. Later that evening, Mr. Cornelius and representatives from Goldman Sachs discussed and corresponded regarding the May 2 MPC Proposal, and confirmed that the exchange ratio to be received by MPC’s affiliates would be 1.0328x in order to achieve a blended exchange ratio of 1.07x.

Later that evening, the ANDX Conflicts Committee held a telephonic meeting with representatives from Goldman Sachs and Sidley. At the meeting, Mr. Cornelius updated the ANDX Conflicts Committee and its advisors of his conversations with Mr. Heminger and Mr. Goff, his understanding of the May 2 MPC Proposal, and his understanding that the May 2 MPC Proposal would be considered by the MPC Board. At this meeting, the ANDX Conflicts Committee agreed to support a transaction based on a 1.135x exchange ratio for the ANDX Public Unitholders, a 1.0328x exchange ratio for MPC’s affiliates, and ANDX distributions continued at the current rate through the effective date of the proposed transaction.

On May 4, 2019, the ANDX Conflicts Committee and representatives from Goldman Sachs and Sidley corresponded regarding the May 2 MPC Proposal, which the ANDX Conflicts Committee understood to require a 1.135x exchange ratio for the ANDX Public Unitholders and 1.0328x exchange ratio for MPC’s affiliates, for a blended exchange ratio of 1.07x, along with an agreement to continue current ANDX distribution levels, and Merger Agreement terms reflecting the same. Later on May 4, 2019, Sidley delivered comments to the Merger Agreement to representatives of Latham & Watkins and Jones Day.

Later that same day, Mr. Cornelius and Mr. Heminger corresponded by email about Merger Agreement terms relating to the continuation of regular ANDX quarterly distributions at the current level prior to the effective time of the proposed transaction. Representatives from Sidley and Jones Day also discussed the same.

On May 4, 2019, at the direction of MPC and the MPLX Conflicts Committee, Latham & Watkins sent a draft of the Support Agreement to Sidley.

On May 5, 2019, Jones Day, Latham & Watkins and Sidley exchanged comments to the draft Merger Agreement and draft Support Agreement, as well as disclosure schedules, and negotiated open terms, including the covenant relating to ANDX distributions.

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On May 6, 2019, Latham & Watkins and Sidley exchanged comments to the draft Merger Agreement and draft Support Agreement, as well as disclosure schedules, and negotiated final terms, including covenants relating to ANDX distributions and an amendment to the omnibus agreement with ANDX. A revised draft Merger Agreement exchanged by the parties included a proposed exchange ratio of 1.135x for the ANDX Public Unitholders and a proposed exchange ratio of 1.0328x for MPC’s affiliates.

On that same day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the proposed merger transaction. Latham & Watkins reviewed with the MPLX Conflicts Committee the terms of the latest draft of the Merger Agreement, including, among other items, closing conditions, representations and warranties, operating covenants and termination provisions. Latham & Watkins also reviewed with the MPLX Conflicts Committee the terms of the Support Agreement and reported on the results of Latham & Watkins’ legal due diligence review of ANDX.

Also on May 6, 2019, the MPC Board approved by way of a unanimous action by written consent the acceptance of a 1.0328x exchange ratio for the ANDX common units held by MPC’s affiliates and also approved the Support Agreement.

On May 7, 2019, the ANDX Conflicts Committee met with representatives of Goldman Sachs and Sidley to review and discuss the proposed transaction. Representatives of Goldman Sachs discussed financial analyses of the proposed transaction. Following the presentation and responses to questions from ANDX Conflicts Committee members, representatives of Goldman Sachs rendered its oral fairness opinion, subsequently confirmed in writing, that, as of May 7, 2019 and based upon and subject to the factors and assumptions set forth therein, the Public Unitholder Exchange Ratio pursuant to the Merger Agreement was fair from a financial point of view to the holders of the Public Unitholder Eligible Units.

Representatives of Sidley then summarized for the ANDX Conflicts Committee the material terms of the Merger Agreement and the Support Agreement. Representatives of Sidley and the ANDX Conflicts Committee then reviewed and discussed reasons for approval of the Merger and the Merger Agreement, and disadvantages relating to the same. The ANDX Conflicts Committee also provided additional feedback on reasons for individual support for the transaction, including risks associated with a standalone strategy. After further discussion with the representatives of Sidley and Goldman Sachs, the ANDX Conflicts Committee, acting in good faith, unanimously (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are in, or not opposed to, the best interests of, ANDX and its subsidiaries treated as a single consolidated entity and the holders of Public Unitholder Eligible Units, (ii) approved and declared advisable the Merger and the consummation of the transactions contemplated by the Merger Agreement, which such approval in (i) and (ii) constituted “Special Approval” under the ANDX Partnership Agreement, and (iii) recommended that the ANDX Board approve the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger.

Later on May 7, 2019, the ANDX Board held a telephonic meeting. Upon the receipt of the recommendation of the ANDX Conflicts Committee, the ANDX Board unanimously determined that the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger, are in, or not opposed to, the best interests of ANDX and its subsidiaries treated as a single consolidated entity, approved and declared advisable the Merger Agreement, the other Transaction Documents to which ANDX and ANDX GP are a party and the transactions contemplated thereby, including the Merger, and resolved to recommend that the holders of ANDX Common Units adopt the Merger Agreement and approve the transactions contemplated thereby, including the Merger, and directed that the Merger Agreement be submitted to the holders of ANDX Common Units for their adoption by written consent.

On that same day, Mr. Helms, on behalf of the MPLX Conflicts Committee, sent a letter dated the same date stating that the MPLX Conflicts Committee was pleased to submit its non-binding proposal of an all-unit transaction with an exchange ratio of 1.135x MPLX Common Units for each outstanding ANDX Common Unit

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that is held by the ANDX Public Unitholders and an exchange ratio of 1.0328x MPLX Common Units for each outstanding ANDX Common Unit held by MPC’s affiliates.

Later that same day, the MPLX Conflicts Committee held a telephonic meeting with representatives of Jefferies and Latham & Watkins to discuss the transaction. Latham & Watkins reviewed with the MPLX Conflicts Committee several updates to the terms of the Merger Agreement and the Support Agreement, including, among other items, the revision of the Support Agreement to include an agreement by MPC to amend ANDX’s existing omnibus agreement to change the definition of a “Partnership Change of Control,” such that the Merger would not provide MPC and its affiliates with an option to terminate certain of their obligations thereunder. Jefferies discussed with the MPLX Conflicts Committee its financial analysis regarding the potential merger transaction and the exchange ratios. Following such discussions, the MPLX Conflicts Committee, in good faith, unanimously (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, were not adverse to the best interests of MPLX and its subsidiaries treated as a single consolidated entity and the MPLX Public Unitholders, (ii) approved the Merger Agreement and the consummation of transactions contemplated thereby, including the Merger, which such approval in (i) and (ii) constituted “Special Approval” under the MPLX Partnership Agreement, and (iii) recommended that the MPLX Board approve the Merger Agreement and the consummation of the transactions contemplated thereby, including the Merger.

Later on May 7, 2019, the MPLX Board held a telephonic meeting. Upon the receipt of the recommendation of the MPLX Conflicts Committee, the MPLX Board unanimously determined that the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger, are not adverse to the best interests of MPLX and its subsidiaries treated as a single consolidated entity, and approved and declared the Merger Agreement, the other Transaction Documents to which MPLX and MPLX GP are a party and the transactions contemplated thereby, including the Merger, advisable.

Later that same day, the parties executed the Merger Agreement and the Support Agreement.

On May 8, 2019, prior to market open, MPC, MPLX and ANDX issued a press release announcing the Merger.

Amended and Restated MPLX Partnership Agreement

The Merger Agreement provides that, prior to the closing, MPC and MPLX will take all actions as are necessary and appropriate to amend and restate the MPLX Partnership Agreement to allow for the creation and issuance of the MPLX Series B Preferred Units, the MPLX Special Limited Partner Interest and the MPLX TexNew Mex Units. The form of the amended and restated MPLX Partnership Agreement is attached to this consent statement/prospectus as Annex C and is incorporated herein by reference. You should read the MPLX Partnership Agreement because it, and not this consent statement/prospectus, is the legal document that, upon its execution and delivery, will govern the rights of MPLX Unitholders following the effective time of the Merger. For additional information regarding the MPLX Partnership Agreement, see “Comparison of Unitholders’ Rights—MPLX Unitholders” beginning on page 139.

Recommendation of the ANDX Board

On May 7, 2019, the ANDX Conflicts Committee unanimously determined that the Merger Agreement and the transactions contemplated thereby are in, or not opposed to, the best interests of ANDX and its Subsidiaries treated as a single consolidated entity and the holders of Public Unitholder Eligible Units, approved the Merger and the consummation of the transactions contemplated thereby (the foregoing constituting “Special Approval” under the ANDX Partnership Agreement), and recommended that the ANDX Board approve the Merger, the Transaction Documents and the consummation of the transactions contemplated thereby (the “ANDX Conflicts Committee Recommendation”).

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Upon receipt of the ANDX Conflicts Committee Recommendation, the ANDX Board unanimously determined that the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger are in, or not opposed to, the best interests of ANDX and its subsidiaries treated as a single consolidated entity, approved the Merger Agreement, the other Transaction Documents to which ANDX and ANDX GP are a party and the transactions contemplated thereby, including the Merger, and resolved to recommend that the holders of ANDX Common Units vote “FOR” the adoption of the Merger Agreement and the approval of the transactions contemplated thereby, including the Merger, a vote “FOR” the Non-Binding Compensation Advisory Proposal, and directed that the Merger Agreement and the Non-Binding Compensation Advisory Proposal be submitted to a vote of holders of ANDX Common Units by written consent.

Reasons for the Recommendation of the ANDX Board

The ANDX Board consulted with its legal advisors and financial advisors and considered many factors in its evaluation of the Merger. The ANDX Board considered the following factors to be generally positive or favorable in making its determination and approvals with respect to the Merger and its related recommendation to the ANDX unitholders:

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The ANDX Board considered the following factors to be generally negative or unfavorable in making its determination and approvals with respect to the Merger and the related recommendation to the holders of ANDX Common Units:

The foregoing discussion of the information and factors considered by the ANDX Board is not intended to be exhaustive, but includes material factors the ANDX Board considered. In view of the variety of factors considered in connection with its evaluation of the Merger and the complexity of these matters, the ANDX Board did not find it useful and did not attempt to quantify or assign any relative or specific weights to the various factors considered in making its determination and recommendation. In addition, each of the members of the ANDX Board may have given differing weights to different factors. Overall, the ANDX Board believed that the positive factors supporting the Merger outweighed the negative factors it considered.

The explanation of the reasoning of the ANDX Board and certain information presented in this section are forward-looking in nature and, therefore, the information should be read in light of the factors discussed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 26.

Opinion of Financial Advisor to the ANDX Conflicts Committee

Goldman Sachs rendered its opinion to the ANDX Conflicts Committee that, as of May 7, 2019 and based upon and subject to the factors and assumptions set forth therein, the Public Unitholder Exchange Ratio pursuant to the Merger Agreement was fair from a financial point of view to the ANDX Public Unitholders.

The full text of the written opinion of Goldman Sachs, dated May 7, 2019, which sets forth assumptions made, procedures followed, matters considered and limitations on the review undertaken in connection with the opinion, is attached as Annex B to this consent statement/prospectus. Goldman Sachs provided advisory services and its opinion for the information and assistance of the ANDX Conflicts Committee in connection with its consideration of the Merger. The Goldman Sachs opinion is not a recommendation as to how any ANDX Public Unitholder should vote with respect to the Merger, or any other matter.

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In connection with rendering the opinion described above and performing its related financial analyses, Goldman Sachs reviewed, among other things:

Goldman Sachs also held discussions with members of the ANDX Conflicts Committee and the managements of ANDX, MPLX and MPC regarding their respective assessment of the strategic rationale for, and the potential benefits of, the Merger and the past and current business operations, financial condition and future prospects of ANDX and MPLX; reviewed the reported price and trading activity for ANDX Common Units and MPLX Common Units; compared certain financial and stock market information for ANDX and MPLX with similar information for certain other companies the securities of which are publicly traded; and performed such other studies and analyses, and considered such other factors, as it deemed appropriate.

For purposes of rendering this opinion, Goldman Sachs, with the ANDX Conflicts Committee’s consent, relied upon and assumed the accuracy and completeness of all of the financial, legal, regulatory, tax, accounting and other information provided to, discussed with or reviewed by it without assuming any responsibility for independent verification thereof. In that regard, Goldman Sachs assumed with the ANDX Conflicts Committee’s consent that the Forecasts, including the Synergies Forecast, were reasonably prepared on a basis reflecting the best currently available estimates and judgments of the ANDX Conflicts Committee. Goldman Sachs did not make an independent evaluation or appraisal of the assets and liabilities (including any contingent, derivative or other off-balance-sheet assets and liabilities) of ANDX or MPLX or any of their respective subsidiaries and it was not furnished with any such evaluation or appraisal. Goldman Sachs assumed that all governmental, regulatory or other consents and approvals necessary for the consummation of the Merger will be obtained without any adverse effect on ANDX or MPLX or on the expected benefits of the Merger in any way meaningful to its analysis. Goldman Sachs has also assumed that the Merger will be consummated on the terms set forth in the Merger Agreement without the waiver or modification of any term or condition the effect of which would be in any way meaningful to its analysis.

Goldman Sachs’ opinion does not address the underlying business decision of ANDX to engage in the Merger, or the relative merits of the Merger as compared to any strategic alternatives that may be available to ANDX; nor does it address any legal, regulatory, tax or accounting matters. Goldman Sachs was not requested to solicit, and did not solicit, interest from other parties with respect to an acquisition of, or other business

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combination with, ANDX or any alternative transaction. Goldman Sachs’ opinion addresses only the fairness from a financial point of view to the holders of the Public Unitholder Eligible Units, as of the date of the opinion, of the Public Unitholder Exchange Ratio pursuant to the Merger Agreement. Goldman Sachs’ opinion does not express any view on, and does not address, any other term or aspect of the Merger Agreement or the Merger or any term or aspect of any other agreement or instrument contemplated by the Merger Agreement or entered into or amended in connection with the Merger, including the conversion of Affiliated Unitholder Eligible Units into the right to receive MPLX Common Units or the Affiliated Unitholder Exchange Ratio, any allocation of the aggregate consideration payable pursuant to the Merger Agreement, including between the holders of Public Unitholder Eligible Units and holders of Affiliated Unitholder Eligible Units, the fairness of the Merger to, or any consideration received in connection therewith by, the holders of any other class of securities, creditors or other constituencies of ANDX; nor as to the fairness of the amount or nature of any compensation to be paid or payable to any of the officers, directors or employees of ANDX, or any class of such persons in connection with the Merger, whether relative to the Public Unitholder Exchange Ratio pursuant to the Merger Agreement or otherwise. Goldman Sachs does not express any opinion as to the prices at which the MPLX Common Units will trade at any time or as to the impact of the Merger on the solvency or viability of ANDX or MPLX or the ability of ANDX or MPLX to pay their respective obligations when they come due. Goldman Sachs’ opinion was necessarily based on economic, monetary, market and other conditions as in effect on, and the information made available to it as of, the date of the opinion and Goldman Sachs assumed no responsibility for updating, revising or reaffirming its opinion based on circumstances, developments or events occurring after the date of its opinion. Goldman Sachs’ opinion was approved by a fairness committee of Goldman Sachs.

The following is a summary of the material financial analyses delivered by Goldman Sachs to the ANDX Conflicts Committee in connection with rendering the opinion described above. The following summary, however, does not purport to be a complete description of the financial analyses performed by Goldman Sachs, nor does the order of analyses described represent relative importance or weight given to those analyses by Goldman Sachs. Some of the summaries of the financial analyses include information presented in tabular format. The tables must be read together with the full text of each summary and are alone not a complete description of Goldman Sachs’ financial analyses. Except as otherwise noted, the following quantitative information, to the extent that it is based on market data, is based on market data as it existed on or before May 3, 2019, the second to last trading day before the meeting of the ANDX Conflicts Committee that approved the Merger, and is not necessarily indicative of current market conditions.

Implied Exchange Ratio Analysis; Historical Stock Trading Analysis. Goldman Sachs reviewed the historical trading prices for the ANDX Common Units and the MPLX Common Units from April 27, 2018 to May 3, 2019 and calculated historical exchange ratios for the ANDX Common Units by dividing the closing price per ANDX Common Unit by the closing price per MPLX Common Unit for each day during the following periods: (i) the twelve-month period ended May 3, 2019; (ii) April 30, 2018, the first trading day after the announcement of MPC’s acquisition of Andeavor, through May 3, 2019; (iii) August 6, 2018, the last trading day before the closing of ANDX’s $1.6 billion dropdown transaction, through May 3, 2019; (iv) the six-month period ended May 3, 2019; and (v) October 26, 2018, the first trading day after the announcement of the change in ANDX’s distribution policy, through May 3, 2019. The following table presents the results of this analysis:

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Illustrative Discounted Cash Flow Analysis—ANDX Standalone.

Using the ANDX Standalone Forecast, Goldman Sachs performed an illustrative discounted cash flow analysis of the ANDX Common Units on a standalone basis. Using discount rates ranging from 6.0% to 7.5%, reflecting estimates of ANDX’s weighted average cost of capital, Goldman Sachs discounted to present value as of December 31, 2018 (i) estimates of unlevered free cash flow for ANDX for fiscal years 2019 through 2023, as reflected in the ANDX Standalone Forecast and (ii) a range of illustrative terminal values for ANDX, which were calculated by applying an illustrative terminal value to EBITDA multiple range of 9.5x to 12.0x to estimated terminal year EBITDA for ANDX, which estimated terminal year EBITDA was approved for Goldman Sachs’ use by the ANDX Conflicts Committee. Goldman Sachs derived such discount rate range by application of the Capital Asset Pricing Model (“CAPM”), which requires certain partnership-specific inputs, including the partnership’s target capital structure weightings, the cost of long-term debt, after-tax yield on permanent excess cash, if any, future applicable marginal cash tax rate and a beta for the partnership, as well as certain financial metrics for the United States financial markets generally. The illustrative terminal value to EBITDA multiple ranges for ANDX were derived by Goldman Sachs using its professional judgment and experience, taking into account, among other things, EBITDA multiples implied by ANDX’s trading prices and next 12 months’ EBITDA as reported by ANDX over certain prior periods. Goldman Sachs derived a range of illustrative enterprise values for ANDX on a standalone basis by adding the ranges of illustrative present values it derived above. Goldman Sachs then subtracted from the range of illustrative enterprise values it derived for ANDX the amount of net debt and preferred equity for ANDX as of December 31, 2018 as reported by ANDX to derive a range of illustrative equity values. Goldman Sachs then divided the range of illustrative equity values it derived by the number of fully diluted outstanding units of ANDX, as provided by the management of ANDX and approved for Goldman Sachs’ use by the ANDX Conflicts Committee, to derive a range of illustrative present values per ANDX Common Unit on a standalone basis of $42.56 to $61.28.

Illustrative Discounted Cash Flow Analysis—Implied Valuation Uplift.

Using the MPLX Pro Forma Forecast, Goldman Sachs performed an illustrative discounted cash flow analysis on the MPLX Common Units pro forma for the Merger and calculated the implied valuation uplift for the Public Unitholder Eligible Units upon consummation of the Merger. Using (i) discount rates ranging from 6.0% to 7.5% (referred to in this section as the “Standalone DCF Discount Rate Range”), reflecting estimates of the weighted average cost of capital of ANDX on a standalone basis, and (ii) discount rates ranging from 5.5% to 7.0% (referred to in this section as the “Blended DCF Discount Rate Range”), reflecting estimates of the blended weighted average cost of capital of each of ANDX and MPLX on a standalone basis, Goldman Sachs discounted to present value as of December 31, 2018 (i) estimates of unlevered free cash flow for MPLX pro forma for the Merger (including free cash flow resulting from the estimated synergies as reflected in the Synergies Forecast) for the years 2019 through 2023, as reflected in the MPLX Pro Forma Forecast and (ii) a range of illustrative terminal values for MPLX pro forma for the Merger, which were calculated by applying an illustrative terminal value to EBITDA multiple range of 9.5x to 12.0x to estimated terminal year EBITDA for MPLX pro forma for the Merger, which estimated terminal year EBITDA was approved for Goldman Sachs’ use by the ANDX Conflicts Committee. Goldman Sachs derived such discount rate range by application of CAPM, which requires certain partnership-specific inputs, including the partnership’s target capital structure weightings, the cost of long-term debt, after-tax yield on permanent excess cash, if any, future applicable marginal cash tax rate and a beta for the partnership, as well as certain financial metrics for the United States financial markets generally. The illustrative terminal value to EBITDA multiple ranges for MPLX pro forma for the Merger were derived by Goldman Sachs using its professional judgment and experience, taking into account, among other things, EBITDA multiples implied by trading prices for ANDX and MPLX and next-12 months’ EBITDA as reported by ANDX and MPLX over certain prior periods. Goldman Sachs derived a range of illustrative enterprise values for MPLX pro forma for the Merger by adding the ranges of illustrative present values it derived above. Goldman Sachs then subtracted from the range of illustrative enterprise values it derived for MPLX pro forma for the Merger the estimated amount of net debt and nonconvertible preferred equity for MPLX pro forma for the Merger and book values of MPLX’s non-controlling interests, in each case as of December 31, 2018 and as

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reported by MPLX to derive a range of illustrative equity values for MPLX pro forma for the Merger. Goldman Sachs then divided the range of illustrative equity values it derived by the number of fully diluted outstanding units of MPLX pro forma for the Merger, as provided by the management of MPC and approved for Goldman Sachs’ use by the ANDX Conflicts Committee, to derive a range of illustrative present values per MPLX Common Unit pro forma for the Merger. Goldman Sachs then calculated a range of illustrative implied values for the pro forma value to be received per Public Unitholder Eligible Unit pursuant to the Merger Agreement by multiplying the implied price per MPLX Common Units pro forma for the Merger derived from the above analysis by the Public Unitholder Exchange Ratio. This analysis resulted in a range of illustrative implied values for the pro forma value to be received per Public Unitholder Eligible Unit pursuant to the Merger Agreement of (i) $43.66 to $61.84 using the Standalone DCF Discount Rate Range and (ii) $45.01 to $63.63 using the Blended DCF Discount Rate Range.

Illustrative Present Value of Future Unit Price Analysis—ANDX GP Standalone.

Goldman Sachs performed an illustrative analysis of the implied present values of illustrative future values per ANDX Common Unit, which is designed to provide an indication of the present value of a theoretical future value of an entity’s equity as a function of such entity’s financial multiples. Goldman Sachs first calculated the illustrative implied value per ANDX Common Unit on a standalone basis as of December 31, 2022 by applying a range of illustrative EV/EBITDA multiples of 9.5x to 12.0x to estimated EBITDA for ANDX for fiscal year 2022, as reflected in the ANDX Standalone Forecast. The illustrative multiple estimates were derived by Goldman Sachs utilizing its professional judgment and experience, taking into account current and historical trading data and illustrative multiple estimates for ANDX and MPLX. To derive illustrative implied equity values per ANDX Common Unit on a standalone basis, Goldman Sachs subtracted from the range of illustrative enterprise values it derived for ANDX on a standalone basis the amount of ANDX’s net debt as of December 31, 2022 as reflected in the ANDX Standalone Forecast and the book value of ANDX’s preferred equity as of December 31, 2022 as approved for Goldman Sachs’ use by the ANDX Conflicts Committee. Goldman Sachs then divided the range of illustrative equity values it derived by the number of fully diluted outstanding units of ANDX on a standalone basis, as provided by ANDX management and approved for Goldman Sachs’ use by the ANDX Conflicts Committee to derive a range of illustrative values per ANDX Common Unit on a standalone basis as of December 31, 2022. Goldman Sachs then discounted to present value as of December 31, 2018, using a range of illustrative discount rates of 7.0% to 8.0%, reflecting an estimate of ANDX’s cost of equity, the sum of (i) the theoretical future value of ANDX Common Units as of December 31, 2022 and (ii) the aggregate per unit distributions estimated for each of the fiscal years 2019 to 2022 as reflected in the ANDX Standalone Forecast. Goldman Sachs derived such discount rate range by application of CAPM, which requires certain entity-specific inputs, including a beta for the entity, as well as certain financial metrics for the United States financial markets generally. This analysis resulted in a range of illustrative implied present values per ANDX Common Unit of $43.61 to $59.77.

Illustrative Present Value of Future Unit Price Analysis—Implied Valuation Uplift.

Goldman Sachs performed an illustrative analysis of the implied present values of illustrative future values per MPLX Common Unit pro forma for the Merger and calculated the implied valuation uplift for ANDX Common Units upon consummation of the Merger. Goldman Sachs first calculated the illustrative implied value per MPLX Common Unit pro forma for the Merger as of December 31, 2022 by applying a range of illustrative EV/EBITDA multiples of 9.5 to 12.0 to estimated EBITDA of MPLX pro forma for the Merger for fiscal year 2022, as reflected in the MPLX Pro Forma Forecast. The illustrative multiple estimates were derived by Goldman Sachs utilizing its professional judgment and experience, taking into account current and historical trading data and illustrative EV/EBITDA multiple estimates for ANDX and MPLX. To derive illustrative implied equity values per MPLX Common Unit pro forma for the Merger, Goldman Sachs subtracted from the range of illustrative enterprise values it derived for MPLX pro forma for the Merger the amount of MPLX’s net debt and nonconvertible preferred equity pro forma for the Merger as of December 31, 2022 as reflected in the MPLX Pro

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Forma Forecast and book value of MPLX’s non-controlling interests as of December 31, 2022 as approved for Goldman Sachs’ use by the ANDX Conflicts Committee. Goldman Sachs then divided the range of illustrative equity values it derived by the number of fully diluted outstanding units of MPLX pro forma for the Merger, as provided by MPC management and approved for Goldman Sachs’ use by the ANDX Conflicts Committee to derive a range of illustrative values per MPLX Common Unit as of December 31, 2022. Goldman Sachs then discounted to present value as of December 31, 2018, using (i) a range of illustrative discount rates of 7.0% to 8.0% (referred to in this section as the “Standalone PV of FUP Discount Rate Range”), reflecting an estimate of ANDX’s cost of equity on a standalone basis and (ii) a range of illustrative discount rates of 6.5% to 7.5% (referred to in this section as the “Blended PV of FUP Discount Rate Range”), reflecting estimates of the blended cost of equity of each of ANDX and MPLX on a standalone basis, the sum of (i) the theoretical future value of MPLX Common Units pro forma for the Merger as of December 31, 2022 and (ii) the aggregate per unit distributions estimated for each of the years 2019 to 2022, as reflected in the MPLX Pro Forma Forecast to derive a range or illustrative implied present values per MPLX Common Unit pro forma for the Merger. Goldman Sachs also discounted to present value as of December 31, 2018, using the Standalone PV of FUP Discount Rate Range and the Blended PV of FUP Discount Rate Range, the distribution per ANDX Common Unit paid by ANDX for the first quarter of 2019. Goldman Sachs derived such discount rate range by application of CAPM, which requires certain entity-specific inputs, including a beta for the entity, as well as certain financial metrics for the United States financial markets generally. Goldman Sachs then calculated a range of illustrative implied values for the pro forma value to be received per Public Unitholder Eligible Unit pursuant to the Merger Agreement by adding (i) the product obtained by multiplying the implied present values per MPLX Common Units pro forma for the Merger derived from the above analysis by the Public Unitholder Exchange Ratio and (ii) implied present value of the distribution per ANDX Common Unit paid by ANDX for the first quarter of 2019. This analysis resulted in a range of illustrative implied present values for the pro forma value to be received per Public Unitholder Eligible Unit pursuant to the Merger Agreement of (i) $44.76 to $60.56 using the Standalone PV of FUP Discount Rate Range and (ii) $45.49 to $61.59 using the Blended PV of FUP Discount Rate Range.

Illustrative Contribution Analysis. Goldman Sachs analyzed the implied contribution of ANDX (calculated based on the relative contributions of the Public Unitholder Eligible Units and the Affiliated Unitholder Eligible Units) and MPLX to the pro forma combined partnership using (i) an illustrative standalone equity value for ANDX and MPLX, calculated using the closing price per ANDX Common Unit and MPLX Common Unit as of May 3, 2019 and the number of fully diluted outstanding ANDX Common Units and MPLX Common Units as provided by management of ANDX and MPLX, respectively, and approved for Goldman Sachs’ use by the ANDX Conflicts Committee, (ii) estimated EBITDA for fiscal years 2019 through 2021, as reflected in the ANDX Forecast and the MPLX Forecast, respectively, and (iii) estimated distributable cash flow for fiscal years 2019 through 2021, as reflected in the ANDX Forecast and the MPLX Forecast, respectively.

The following table presents the results of this analysis:

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Pro Forma Merger Analysis. Goldman Sachs prepared illustrative pro forma analyses of the potential financial impact of the Merger using the ANDX Standalone Forecast and the MPLX Pro Forma Forecast. For each of the calendar years 2019 to 2023 Goldman Sachs compared the distributable cash flows per ANDX Common Unit on a standalone basis and the distributions per ANDX Common Unit on a standalone basis to the distributable cash flows per MPLX Common Unit pro forma for the Merger represented by the Public Unitholder Exchange Ratio and the distributions per MPLX Common Unit pro forma for the Merger represented by the Public Unitholder Exchange Ratio. The following table presents the results of this analysis, which indicated the Merger would be accretive to the holders of Public Unitholder Eligible Units on the basis of distributable cash flows per ANDX Common Unit and dilutive to the holders of Public Unitholder Eligible Units on the basis of distributions per ANDX Common Unit:

The preparation of a fairness opinion is a complex process and is not necessarily susceptible to partial analysis or summary description. Selecting portions of the analyses or of the summary set forth above, without considering the analyses as a whole, could create an incomplete view of the processes underlying Goldman Sachs’ opinion. In arriving at its fairness determination, Goldman Sachs considered the results of all of its analyses and did not attribute any particular weight to any factor or analysis considered by it. Rather, Goldman Sachs made its determination as to fairness on the basis of its experience and professional judgment after considering the results of all of its analyses.

Goldman Sachs prepared these analyses for purposes of Goldman Sachs’ providing its opinion to the ANDX Conflicts Committee as to the fairness from a financial point of view to the holders of Public Unitholder Eligible Units, as of the date of the opinion, of the Public Unitholder Exchange Ratio pursuant to the Merger Agreement. These analyses do not purport to be appraisals nor do they necessarily reflect the prices at which businesses or securities actually may be sold. Analyses based upon forecasts of future results are not necessarily indicative of actual future results, which may be significantly more or less favorable than suggested by these analyses. Because these analyses are inherently subject to uncertainty, being based upon numerous factors or events beyond the control of the parties or their respective advisors, none of ANDX, MPLX, Goldman Sachs or any other person assumes responsibility if future results are materially different from those forecast.

The applicable merger consideration was determined through arm’s-length negotiations between the ANDX Conflicts Committee, the MPLX Conflicts Committee and MPC and was approved by the ANDX Board. Goldman Sachs provided advice to the ANDX Conflicts Committee during these negotiations. Goldman Sachs did not, however, recommend any specific exchange ratio or amount of consideration to ANDX GP or the ANDX Board or that any specific exchange ratio or amount of consideration constituted the only appropriate exchange ratio and/or amount of consideration for the transaction.

As described above, Goldman Sachs’ opinion to the ANDX Conflicts Committee was one of many factors taken into consideration by the ANDX Conflicts Committee in making its determination to approve the Merger Agreement. The foregoing summary does not purport to be a complete description of the analyses performed by Goldman Sachs in connection with the fairness opinion and is qualified in its entirety by reference to the written opinion of Goldman Sachs attached as Annex B to this consent statement/prospectus.

Goldman Sachs and its affiliates are engaged in advisory, underwriting and financing, principal investing, sales and trading, research, investment management and other financial and non-financial activities and services for various persons and entities. Goldman Sachs and its affiliates and employees, and funds or other entities they manage or in which they invest or have other economic interests or with which they co-invest, may at any time

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purchase, sell, hold or vote long or short positions and investments in securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments of ANDX, MPLX, any of their respective affiliates and third parties, including MPC, an affiliate of ANDX and MPLX, and its affiliates, or any currency or commodity that may be involved in the Merger. Goldman Sachs acted as financial advisor to the ANDX Conflicts Committee in connection with, and participated in certain of the negotiations leading to, the transaction contemplated by the Merger Agreement. Goldman Sachs has provided certain financial advisory and/or underwriting services to ANDX and/or its affiliates from time to time for which the Investment Banking Division of Goldman Sachs has received, and may receive, compensation, including having acted as financial advisor to Andeavor, an affiliate of ANDX, in connection with the merger of ANDX and WNRL and the buy-in of ANDX’s incentive distribution rights in October 2017; as joint bookrunner with respect to the public offering of 3.500% Senior Notes due 2022, 4.250% Senior Notes due 2027 and 5.200% Senior Notes due 2047 (aggregate principal amount $1,750,000,000) by ANDX and Tesoro Logistics Finance Corp., an affiliate of ANDX, in November 2017; as joint bookrunner with respect to the public offering of 6.875% Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units (aggregate principal amount $600,000,000) by ANDX in November 2017; as joint bookrunner with respect to the public offering of 3.800% Senior Notes due 2028 and 4.500% Senior Notes due 2048 (aggregate principal amount $1,000,000,000) by ANDX in December 2017; and as financial advisor to Andeavor in connection with its merger with MPC in October 2018. During the two-year period ended May 7, 2019, Goldman Sachs has recognized compensation for financial advisory and/or underwriting services provided by its Investment Banking Division to ANDX and/or its affiliates of approximately $88.9 million. Goldman Sachs also has provided certain financial advisory and/or underwriting services to MPLX and/or its affiliates from time to time for which the Investment Banking Division of Goldman Sachs has received, and may receive, compensation, including having acted as joint bookrunner with respect to the public offering of 3.375% Senior Notes due 2023, 4.000% Senior Notes due 2028 4.500% Senior Notes due 2038, 4.700% Senior Notes due 2048 and 4.900% Senior Notes due 2058 (aggregate principal amount $5,500,000,000) by MPLX in February 2018. During the two-year period ended May 7, 2019, Goldman Sachs has recognized compensation for financial advisory and/or underwriting services provided by its Investment Banking Division to MPLX and/or its affiliates of approximately $0.9 million. Goldman Sachs may also in the future provide financial advisory and/or underwriting services to ANDX, MPLX and their respective affiliates, for which the Investment Banking Division of Goldman Sachs may receive compensation.

The ANDX Conflicts Committee selected Goldman Sachs as its financial advisor because it is an internationally recognized investment banking firm that has substantial experience in transactions similar to the Merger. Pursuant to a letter agreement dated December 27, 2018 the ANDX Conflicts Committee engaged Goldman Sachs to act as its financial advisor in connection with the contemplated transaction. The engagement letter between the ANDX Conflicts Committee and Goldman Sachs provides for a transaction fee of $4,000,000, $250,000 of which became payable upon the receipt by the ANDX Conflicts Committee of MPLX’s initial acquisition proposal, and the remainder of which is contingent upon consummation of the Merger. Goldman Sachs may receive an additional fee of up to $2,500,000 at the Conflict Committee’s sole discretion. In addition, ANDX GP has agreed to reimburse Goldman Sachs for certain of its expenses, including attorneys’ fees and disbursements, and to indemnify Goldman Sachs and related persons against various liabilities, including certain liabilities under the federal securities laws.

Unaudited Forecasted Financial Information

ANDX and MPLX each prepared unaudited forecasted financial information for the years 2019 through 2023 for each respective entity on a standalone basis. The unaudited forecasted financial information does not give effect to the Merger, including any anticipated synergies or their related costs or expenses. The unaudited forecasted financial information was prepared separately by each of the partnerships using, in some cases, different assumptions, and is not intended to be added together. Adding the unaudited forecasted financial information together for the two partnerships is not intended to represent the results the combined partnership will achieve if the Merger is completed and is not intended to represent forecasted financial information for the combined partnership if the Merger is completed. Neither MPLX nor ANDX, as a matter of course, makes public

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long-term projections as to future earnings or other results due to, among other reasons, the uncertainty of the underlying assumptions and estimates. However, the unaudited forecasted financial information was made available to the MPLX Conflicts Committee, the ANDX Conflicts Committee, MPC, and/or Goldman Sachs in connection with the evaluation of the Merger. The inclusion of the unaudited forecasted financial information set forth below should not be regarded as an indication that any of MPLX, ANDX, MPC, Goldman Sachs or any other recipient of this information considered, or now considers, it to be necessarily predictive of actual future results. Readers of this document are cautioned not to place undue reliance on the unaudited forecasted financial information.

The unaudited forecasted financial information was, in general, prepared solely for internal use and is subjective in many respects. As a result, there can be no assurance that the forecasted results will be realized or that actual results will not be significantly higher or lower than estimated. Since the unaudited forecasted financial information covers multiple years, such information by its nature becomes less predictive with each successive year. The estimates and assumptions underlying the unaudited forecasted financial information involve judgments with respect to, among other things, future economic, competitive, regulatory and financial market conditions which may not materialize and that are inherently subject to significant uncertainties and contingencies, all of which are difficult to predict and many of which are beyond the control of MPLX, ANDX and/or MPC and will be beyond the control of the combined entity. ANDX Unitholders are urged to review the SEC filings of MPLX and ANDX for a description of risk factors with respect to the respective businesses of MPLX and ANDX. See the sections entitled “Cautionary Statement Regarding Forward-Looking Statements” and “Where You Can Find More Information” beginning on pages 26 and 172, respectively. The unaudited forecasted financial information was not prepared with a view toward public disclosure, nor was it prepared with a view toward compliance with published guidelines of the SEC or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of prospective financial information but, in the view of each of MPLX’s and ANDX’s management, as applicable, was prepared on a reasonable basis, reflected the best available estimates and judgments as of the date of preparation, and presents, to the best of management’s knowledge and belief, the expected course of action and the expected future financial performance of MPLX and ANDX, as applicable. However, this information is not fact and should not be relied upon as being necessarily indicative of future results, and readers of this consent statement/prospectus are cautioned not to place undue reliance on the unaudited forecasted financial information. The unaudited forecasted financial information included in this document has been prepared by, and is the responsibility of MPLX’s and ANDX’s management. None of the independent accountants of MPLX or ANDX nor any other independent accountants, have audited, reviewed, examined, compiled or applied agreed-upon procedures with respect to the accompanying unaudited forecasted financial information and, accordingly, the independent accountants do not express an opinion or any other form of assurance with respect thereto.

The PricewaterhouseCoopers LLP report incorporated by reference in this consent statement/prospectus relates to MPLX’s previously issued financial statements. The Ernst & Young LLP report incorporated by reference in this consent statement/prospectus relates to ANDX’s previously issued financial statements. None of the foregoing reports extend to the unaudited forecasted financial information and should not be read to do so.

NEITHER MPLX NOR ANDX HAVE UPDATED OR INTEND TO UPDATE OR OTHERWISE REVISE THE UNAUDITED FORECASTED FINANCIAL INFORMATION TO REFLECT CIRCUMSTANCES EXISTING AFTER THE DATE WHEN MADE OR TO REFLECT THE OCCURRENCE OF FUTURE EVENTS, EVEN IN THE EVENT THAT ANY OR ALL OF THE ASSUMPTIONS UNDERLYING SUCH PROSPECTIVE FINANCIAL INFORMATION ARE NO LONGER APPROPRIATE.

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ANDX. The following table presents select unaudited forecasted financial information of ANDX for fiscal year 2019 through fiscal year 2023 prepared by management of ANDX GP, which is referred to as the ANDX unaudited forecasted financial information:

Distributable Cash Flow Summary

The ANDX unaudited forecasted financial information is based on various assumptions, including the following principal assumptions:

The estimates and assumptions underlying the ANDX unaudited forecasted financial information are inherently uncertain and, though considered reasonable by ANDX GP as of the date of the preparation of such unaudited forecasted financial information, are subject to a wide variety of significant business, economic, regulatory and competitive risks and uncertainties that could cause actual results to differ materially from those contained in the unaudited forecasted financial information, including, among other things, the matters described in the sections entitled “Cautionary Statement Regarding Forward-Looking Statements” and “Risk Factors” beginning on pages 26 and 28, respectively. Accordingly, there can be no assurance that the unaudited forecasted financial information is necessarily predictive of the actual future performance of ANDX, or that actual results will not differ materially from those presented in the ANDX unaudited forecasted financial information. Inclusion of the ANDX unaudited forecasted financial information in this consent statement/prospectus should not be regarded as a representation by any person that the results contained in the ANDX unaudited forecasted financial information will be achieved.

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The ANDX unaudited forecasted financial information is not included in this consent statement/prospectus in order to induce any ANDX unitholder to consent to the Merger.

MPLX. The following table presents select unaudited forecasted financial information of MPLX for fiscal year 2019 through fiscal year 2023 prepared by management of MPLX GP, which is referred to as the MPLX unaudited forecasted financial information:

Distributable Cash Flow Summary

The MPLX unaudited forecasted financial information is based on various assumptions, including the following principal assumptions:

The estimates and assumptions underlying the MPLX unaudited forecasted financial information are inherently uncertain and, though considered reasonable by the management of MPLX GP as of the date of the preparation of such unaudited forecasted financial information, are subject to a wide variety of significant business, economic, regulatory and competitive risks and uncertainties that could cause actual results to differ materially from those contained in the unaudited forecasted financial information, including, among other things, the matters described in the sections entitled “Cautionary Statement Regarding Forward-Looking Statements” and “Risk Factors” beginning on pages 26 and 28, respectively. The unaudited forecasted financial information included in this document has been prepared by, and is the responsibility of, MPLX’s management. PricewaterhouseCoopers LLP has not audited, reviewed, examined, compiled nor applied agreed-upon procedures with respect to the accompanying unaudited forecasted financial information and, accordingly, PricewaterhouseCoopers LLP does not express an opinion or any other form of assurance with respect thereto. The unaudited forecasted financial

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information was not prepared with a view toward compliance with published guidelines of the SEC or the guidelines established by the American Institute of Certified Public Accountants for preparation or presentation of prospective financial information. Accordingly, there can be no assurance that the forecasted results are necessarily predictive of the actual future performance of MPLX, or that actual results will not differ materially from those presented in the MPLX unaudited forecasted financial information. Inclusion of the MPLX unaudited forecasted financial information in this consent statement/prospectus should not be regarded as a representation by any person that the results contained in the MPLX unaudited forecasted financial information will be achieved. The PricewaterhouseCoopers LLP report incorporated by reference in this consent statement/prospectus relates to MPLX’s previously issued financial statements. It does not extend to the unaudited forecasted financial information and should not be read to do so.

Synergies Forecast

In connection with the ANDX and MPLX standalone forecasts, management of MPC also projected $25.0 million of annual cost synergies to result from the Merger.

The MPLX unaudited forecasted financial information is not included in this consent statement/prospectus in order to induce any ANDX unitholder to consent to the Merger.

Recommendation of the MPLX Board

The MPLX Conflicts Committee, with the advice and assistance of its financial and legal advisors, negotiated, evaluated, and, at a meeting held on May 7, 2019, unanimously approved the Merger Agreement and the consummation of the transactions contemplated thereby, including the Merger.

In reaching its decision to approve the Merger Agreement and the consummation of the transactions contemplated thereby, including the Merger, and to recommend that the MPLX Board approve the Merger Agreement and the consummation of the transactions contemplated thereby, including the Merger (the “MPLX Conflicts Committee Recommendation”), the MPLX Conflicts Committee consulted extensively with its financial and legal advisors and MPLX’s management. After such discussions, the MPLX Conflicts Committee unanimously determined that the Merger Agreement and the transactions contemplated thereby, including the Merger, are not adverse to the best interests of MPLX and its subsidiaries treated as a consolidated entity and the holders of MPLX Common Units (other than MPLX GP and its affiliates, including MPC).

Upon receipt of the MPLX Conflicts Committee Recommendation, the MPLX Board unanimously determined that the Merger Agreement, the other Transaction Documents and the transactions contemplated thereby, including the Merger are not adverse to the best interests of MPLX and its subsidiaries treated as a consolidated entity, and approved and declared the Merger Agreement, the other Transaction Documents to which MPLX and MPLX GP are a party and the transactions contemplated thereby, including the Merger, advisable.

Reasons of the MPLX Board for the Merger

The MPLX Board’s decision to approve the Merger Agreement and the transactions contemplated thereby, including the Merger, was based on a number of factors, including the following (which are not necessarily presented in order of relative importance):

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The MPLX Board considered all of these factors as a whole and unanimously concluded that they supported a determination to approve the Merger Agreement, the Merger and the other transactions contemplated thereby. The foregoing discussion of the information and factors considered by the MPLX Board is not exhaustive. In view of the wide variety of factors considered by the MPLX Board in connection with its evaluation of the Merger and the complexity of these matters, the MPLX Board did not consider it practical to, nor did it attempt to, quantify, rank or otherwise assign relative weights to the specific factors that it considered in reaching its decision. In considering the factors described above and any other factors, individual members of the MPLX Board may have viewed factors differently or given different weight or merit to different factors.

The foregoing discussion of the information and factors considered by the MPLX Board is forward-looking in nature. This information should be read in light of the factors described in the section entitled “Cautionary Statement Regarding Forward-Looking Statements” beginning on page 26.

Regulatory Approvals

In connection with the Merger, MPLX intends to make all required filings under the Securities Act and the Exchange Act, as well as any required filings or applications with the NYSE. MPLX and ANDX are unaware of any other requirement for the filing of information with, or the obtaining of the approval of, governmental authorities in any jurisdiction that is applicable to the Merger.

The Merger is not reportable under the HSR Act, and therefore, no filings with respect to the Merger were required with the FTC or the DOJ.

MPC’s Ownership Interest In and Control of ANDX and MPLX

ANDX unitholders should be aware that each of ANDX and MPLX is controlled by MPC through MPC’s indirect 100% ownership of ANDX GP, which owns 100% of the non-economic general partner interest in ANDX, and MPLX GP, which owns 100% of the non-economic general partner interest in MPLX. As a result, MPC appoints the members of both the ANDX Board and the MPLX Board, in each case a majority of whom are affiliated with MPC and its affiliates, and thereby could be seen as controlling all of ANDX’s and MPLX’s decisions, other than those involving certain conflicts of interest with MPC or that require an affirmative vote of holders of the limited partner interests in ANDX or MPLX pursuant to and in the percentages specified by the ANDX Partnership Agreement or the MPLX Partnership Agreement, as applicable. In addition, as of the Record Date, MPC indirectly owned (i) approximately 64% of the outstanding ANDX Common Units and (ii) approximately 64% of the outstanding MPLX Common Units. Following the closing of the Merger, MPC will indirectly own approximately 63% of the outstanding MPLX Common Units, not including any MPLX Common Units issuable upon conversion of the MPLX Series A Preferred Units or in respect of Converted MPLX Phantom Units, and all of the MPLX TexNew Mex Units and the MPLX Special Limited Partner Interest and continue to indirectly own 100% of the membership interests of ANDX GP and MPLX GP.

Certain directors and executive officers associated with MPC have a relationship with ANDX and MPLX. Gary R. Heminger is Chairman of the Board and Chief Executive Officer of MPC, Chairman of the MPLX Board

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and Chief Executive Officer of MPLX GP and Chairman of the ANDX Board and Chief Executive Officer of ANDX GP. Timothy T. Griffith is Senior Vice President and Chief Financial Officer of MPC and a member of the MPLX Board and the ANDX Board. Donald C. Templin is President, Refining, Marketing and Supply of MPC and a member of the MPLX Board and the ANDX Board. Gregory J. Goff is Executive Vice Chairman of MPC and a member of the MPLX Board and the ANDX Board. Certain of the foregoing persons also serve as officers, directors and/or members of management of other affiliates of MPC.

Interests of Directors and Executive Officers of ANDX GP in the Merger

In considering the recommendation of the ANDX Conflicts Committee, ANDX Common Unitholders should be aware that the directors and executive officers of ANDX GP may have interests in the Merger and related transactions, that are different from, or in addition to, the interests of ANDX Unitholders generally. With respect to at least some of the directors and executive officers, these interests include, but are not limited to, positions as directors or officers of MPC, MPLX GP and their respective affiliates; the treatment in the Merger of ANDX Phantom Units held by ANDX GP executive officers and directors; equity holdings in MPC or MPLX; and rights to ongoing indemnification and insurance coverage. These interests are described in more detail below, and certain of them are quantified in the narrative and tabular disclosure included in the section entitled “—Merger-Related Compensation” beginning on page 77.

The members of the ANDX Conflicts Committee were aware of and considered these interests, among other matters, in evaluating and negotiating the Merger Agreement, in approving the Merger and in determining to recommend to ANDX Common Unitholders that they consent to the adoption of the Merger Agreement. ANDX Common Unitholders should take these interests into account in deciding whether to consent to the adoption of the Merger Agreement.

The directors and executive officers of MPLX GP, in their capacity as such, do not have interests in the Merger and related transactions that are different from, or in addition to, the interests of MPLX Unitholders generally.

Treatment of ANDX Phantom Units and ANDX Director Phantom Units

Assumption and Potential Double-Trigger Acceleration of ANDX Phantom Units

As described below in the section titled “The Merger Agreement—Treatment of ANDX Phantom Units in the Merger” beginning on page 82, any ANDX Phantom Units, other than any ANDX Director Phantom Unit, will be assumed by MPLX and converted into phantom units denominated in MPLX Common Units. Pursuant to their pre-existing terms, these awards, with the exception of the March 1, 2019 ANDX Phantom Units award to Don J. Sorenson (the “2019 Sorenson ANDX Phantom Units Award”), will vest upon a qualifying termination of employment of the holder within two years following the October 1, 2018, closing date of MPC’s acquisition of Andeavor, which transaction constituted a change in control of ANDX (the “Prior CIC”). The 2019 Sorenson ANDX Phantom Units Award does not provide for the full vesting of the award upon a qualified termination of employment of the holder within two years of the Prior CIC. Instead, such award provides for full vesting of the award upon a qualified termination of Mr. Sorenson within two years of a change in control of MPC (“MPC CIC”).

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The table below sets forth the number of ANDX Phantom Units held by ANDX GP’s current executive officers as of May 21, 2019 (the assumed date of the closing of the Merger solely for purposes of this “Interests of Directors and Executive Officers of ANDX GP in the Merger” disclosure), which will be assumed by MPLX and will vest upon the earlier of their respective vesting dates or a qualifying termination of employment on the basis of the Prior CIC or an MPC CIC, as applicable. The estimate of the intrinsic value of such awards (on a pre-tax basis) is based on a price per unit of $35.11, which is the average closing market price of ANDX Common Units over the first five business days following the public announcement of the Merger.

As of May 21, 2019, none of the other executive officers of ANDX GP since January 1, 2018, which include Gary R. Heminger, Suzanne Gagle, Blane W. Peery, D. Andrew Woodward, Steven M. Sterin, Kim K.W. Rucker, and Stephan E. Tompsett, hold any ANDX Phantom Units and none is entitled to any compensation that is based on or otherwise relates to the Merger.

Cancellation of Awards Held by Directors of ANDX GP

As described below in the section titled “The Merger Agreement—Treatment of ANDX Phantom Units in the Merger” beginning on page 82, any ANDX Director Phantom Unit will automatically be canceled at the effective time of the Merger, and the holder of any ANDX Director Phantom Unit will be entitled to a cash payment equal to (i) the number of ANDX Common Units subject to the ANDX Director Phantom Unit immediately prior to the effective time of the Merger, whether or not vested, multiplied by (ii) the product of (A) the Public Unitholder Exchange Ratio and (B) the average of the volume weighted average price per unit of MPLX Common Units on the NYSE (as reported by Bloomberg L.P. or, if not reported therein, in another authoritative source mutually selected by MPLX and ANDX) on each of the ten consecutive trading days ending with the complete trading day immediately prior to the Closing Date.

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The table below sets forth the number of ANDX Director Phantom Units held by non-executive members of the ANDX Board as of May 21, 2019 (the assumed date of the closing of the Merger solely for purposes of this “Interests of Directors and Executive Officers of ANDX General Partner in the Merger” disclosure), which will be automatically canceled at the effective time of the Merger in exchange for the cash payment described above. The estimate of the intrinsic value of such awards (on a pre-tax basis) is based on a price per unit of $35.11, which is the average closing market price of ANDX Common Units over the first five business days following the public announcement of the Merger.

See the section entitled “—Assumption and Potential Double-Trigger Acceleration of ANDX Phantom Units” above for the treatment of the ANDX Phantom Units held by Mr. Goff. Mr. Goff does not hold any ANDX Director Phantom Units. None of the other non-executive directors of ANDX since January 1, 2018, which include Pamela K.M. Beall, Raymond J. Bromark, Timothy T. Griffith, Michael J. Hennigan, Thomas C. O’Connor, Jeff A. Stevens, Donald C. Templin, and Michael Wiley, hold any ANDX Director Phantom Units and none is entitled to any compensation that is based on or otherwise relates to the Merger.

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Economic Interests of Directors and Executive Officers of ANDX GP in the Other Parties to the Transaction

As described above under the section entitled “—MPC’s Ownership Interest In and Control of ANDX and MPLX,” certain directors and executive officers of ANDX GP have a relationship with one or more of MPC and MPLX GP, including by serving as a director and/or officer of such entities. Through their relationships with these entities and otherwise, certain of these directors and executive officers of ANDX GP hold equity interests in MPC, MPLX or both. In certain circumstances these equity interests are more valuable than the equity interests in ANDX held by such director or executive officer of ANDX GP. Holding these equity interests in MPC or MPLX, each of which is a counterparty with economic interests adverse to ANDX in certain of the transactions contemplated by the Merger Agreement, gives such directors and executive officers of ANDX GP interests in the Merger and related transactions that are different from the interests of ANDX unitholders generally. Set forth in the table below is the number of: (i) shares of MPC common stock, (ii) MPLX Common Units, and (iii) ANDX Common Units beneficially owned by each of the current directors and executive officers of ANDX GP as of May 21, 2019.

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Merger-Related Compensation

This section sets forth the information required by Item 402(t) of Regulation S-K regarding the compensation of each of ANDX GP’s named executive officers that is based on or otherwise relates to the Merger and that will or may become payable to the named executive officers at the closing of the Merger or on a qualifying termination of employment upon or following the consummation of the Merger. This compensation is referred to as “golden parachute” compensation by the applicable SEC disclosure rules, and in this section we use such term to describe the Merger-related compensation payable to ANDX GP named executive officers. The “golden parachute” compensation payable to these individuals is subject to a non-binding advisory vote of ANDX unitholders. The named executive officers of MPLX GP will not receive compensation based on or otherwise relating to the Merger.

As described above, pursuant to the pre-existing terms of the award agreements granted to ANDX GP employees, awards will vest on a double-trigger basis upon a qualifying termination of the individual’s employment within two years following the date of the Prior CIC, except that with regard to the 2019 Sorenson ANDX Phantom Units Award, such award will vest on a double-trigger basis upon Mr. Sorenson’s qualifying termination of employment within two years following the date of an MPC CIC. (Because the 2019 Sorenson ANDX Phantom Units Award does not provide for payment to Mr. Sorenson in connection with the Merger, it is excluded from the table below.) Such awards are not subject to accelerated vesting on a single-trigger basis in connection with the Merger. For details on the treatment of outstanding ANDX Phantom Units, see the section titled “The Merger Agreement—Treatment of ANDX Phantom Units in the Merger” beginning on page 82.

The amounts set forth in the table below assume the following:

The amounts reported in the table below are estimates based on multiple assumptions that may or may not actually occur, including assumptions described in this consent statement/prospectus, and do not reflect compensation actions that may occur following the filing of this consent statement/prospectus, base compensation increases or annual equity award grants in the ordinary course prior to the effective time of the Merger. The amounts reported below also include any equity awards that may vest after May 21, 2019, but before the actual closing of the Merger. As a result, the actual amounts, if any, to be received by an ANDX GP named executive officer may differ materially from the amounts set forth below. In addition, the amounts

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reflected in the table below are attributable to double-trigger arrangements (i.e., the amounts are payable only in the event of a qualifying termination of the named executive officer’s employment during a specified period).