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Filed pursuant to Rule 424(b)(5)
Registration Statement No. 333-198459

CALCULATION OF REGISTRATION FEE

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PROSPECTUS SUPPLEMENT

(To Prospectus Dated August 28, 2014)

15,600,000 Shares

Carrizo Oil & Gas, Inc.

Common Stock

We are offering 15,600,000 shares of our common stock.

Our common stock is listed on the NASDAQ Global Select Market under the symbol “CRZO.” On June 28, 2017, the last reported sale price of our common stock on the NASDAQ Global Select Market was $15.61 per share.

Investing in our common stock involves risks. Please see “Risk Factors” on page S-13 of this prospectus supplement and on page 2 of the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The shares of common stock are expected to be ready for delivery in New York, New York on or about July 3, 2017.

Joint Book-Running Managers

Senior Co-Managers

Co-Managers

June 28, 2017

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Prospectus Supplement

Prospectus

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering of our common stock. The second part is the accompanying prospectus, which gives more general information, some of which may not apply to this offering of common stock. We sometimes refer to the prospectus supplement and the accompanying prospectus, taken together, as “the prospectus.” If the information varies between this prospectus supplement and the accompanying prospectus, you should rely on the information in this prospectus supplement.

This document is not a prospectus for the purposes of the European Union’s Directive 2003/71 (and any amendments thereto) as implemented in member states of the European Economic Area (the “Prospectus Directive”). This document has been prepared on the basis that all offers of shares offered hereby made to persons in the European Economic Area will be made pursuant to an exemption under the Prospectus Directive from the requirement to produce a prospectus in connection with offers of such shares.

The communication of this document and any other document or materials relating to the issue of any shares offered hereby is not being made, and none of such documents or materials have been

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approved, by an authorised person for the purposes of section 21 of the United Kingdom’s Financial Services and Markets Act 2000. Accordingly, such documents and materials are not being distributed to, and must not be passed on to, the general public in the United Kingdom. The communication of such documents and materials as a financial promotion is only being made to those persons in the United Kingdom falling within the definition of investment professionals (as defined in Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (the “Financial Promotion Order”), or within Article 49(2)(a) to (d) of the Financial Promotion Order, or to any other persons to whom it may otherwise lawfully be made under the Financial Promotion Order (all such persons together being referred to as “relevant persons”). In the United Kingdom, the shares offered hereby are only available to, and any investment or investment activity to which this document relates will be engaged in only with, relevant persons. Any person in the United Kingdom that is not a relevant person should not act or rely on this document or any of its contents.

Neither we nor the underwriters have authorized anyone to provide you with any information or to make any representations other than those contained or incorporated by reference in this prospectus supplement or the accompanying prospectus or in any free writing prospectus made available by us. We and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. Neither we nor the underwriters are making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume the information appearing in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the cover of this prospectus supplement and the accompanying prospectus and that any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference. Our business, financial condition, results of operations and prospects may have changed since that date.

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FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus, including the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, contain statements concerning our intentions, expectations, projections, assessments of risks, estimations, beliefs, plans or predictions for the future, objectives, goals, strategies, future events or performance and underlying assumptions and other statements that are not historical facts. These statements are “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, among others, statements regarding:

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You generally can identify our forward-looking statements by the words “anticipate,” “believe,” budgeted,” “continue,” “could,” “estimate,” “expect,” “forecast,” “goal,” “intend,” “may,” “objective,” “plan,” “potential,” “predict,” “projection,” “possible,” “scheduled,” “should,” “guidance” or other similar words. Such statements rely on assumptions and involve risks and uncertainties, many of which are beyond our control, including, but not limited to, those relating to a worldwide economic downturn, availability of financing, our dependence on our exploratory drilling activities, the volatility of and changes in oil and gas prices, the need to replace reserves depleted by production, impairments of proved oil and gas properties, operating risks of oil and gas operations, our dependence on our key personnel, factors that affect our ability to manage our growth and achieve our business strategy, results, delays and uncertainties that may be encountered in drilling, development or production, interpretations and impact of oil and gas reserve estimation and disclosure requirements, activities and approvals of our partners and parties with whom we have alliances, technological changes, capital requirements, the timing and amount of borrowing base determinations (including determinations by lenders) and availability under our revolving credit facility, evaluations of us by lenders under our revolving credit facility, waivers or amendments under our revolving credit facility in connection with acquisitions, including the Pending Acquisition, other actions by lenders and holders of our capital stock, the potential impact of government regulations, including current and proposed legislation and regulations related to hydraulic fracturing, oil and natural gas drilling, air emissions and climate change, regulatory determinations, litigation, competition, the uncertainty of reserve information and future net revenue estimates, failure of the Pending Acquisition to close, market conditions and other factors affecting our ability to complete our senior notes offering and the preferred stock and warrants issuance, integration and other acquisition risks, other factors affecting our ability to reach agreements or complete acquisitions or dispositions, actions by sellers and buyers, effects of purchase price adjustments, availability of equipment and crews, actions by midstream and other industry participants, weather, our ability to obtain permits and licenses, the results of audits and assessments, the failure to obtain certain bank and lease consents, the existence and resolution of title defects, new taxes and impact fees, delays, costs and difficulties relating to our joint ventures, actions by joint venture parties, results of exploration activities, the availability, market conditions and completion of land acquisitions and dispositions, costs of oilfield services, completion and connection of wells and other factors detailed in this prospectus and in our filings with the Securities and Exchange Commission (“SEC”).

We have based our forward-looking statements on our management’s beliefs and assumptions based on information available to our management at the time the statements are made. We caution you that assumptions, beliefs, expectations, intentions and projections about future events may and often do vary materially from actual results. Therefore, we cannot assure you that actual results will not differ materially from those expressed or implied by our forward-looking statements.

Some of the factors that could cause actual results to differ from those expressed or implied in forward-looking statements are described under “Risk Factors” and in other sections of this prospectus and described under “Risk Factors” and elsewhere in the documents that we incorporate by reference into this prospectus, including our Annual Report on Form 10-K for the year ended December 31, 2016, Quarterly Report on Form 10-Q for the quarter ended March 31, 2017, and in our other reports filed with the SEC, and all other documents incorporated by reference into this prospectus. Should one or more of these risks or uncertainties materialize, or should underlying assumptions prove incorrect, actual outcomes may vary materially from those indicated. All subsequent written and oral forward-looking statements attributable to us or persons acting on our behalf are expressly qualified in their entirety by reference to these risks and uncertainties. You should not place undue reliance on our forward-looking statements. Each forward-looking statement speaks only as of the date of the particular statement, and, except as required by law, we undertake no duty to update or revise any forward-looking statement.

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RISK FACTORS

Before making a decision whether to invest in our common stock, you should consider carefully the risks discussed below as well as those described under “Risk Factors” and elsewhere in our Annual Report on Form 10-K for the year ended December 31, 2016, as they may be amended, supplemented or superseded from time to time by other reports that we subsequently file with the SEC and in our other filings with the SEC which are incorporated by reference in this prospectus supplement and the accompanying prospectus, as well as the risks described in the accompanying prospectus. The risks described below are not the only ones that we face. Additional risks not presently known to us or that we currently deem immaterial individually or in the aggregate as well as the additional risks and uncertainties described elsewhere in this prospectus supplement or in the documents incorporated by reference in this prospectus supplement may also adversely affect our business, operating results, financial condition and prospects, as well as the value of an investment in our common stock.

If any of the following risks actually were to occur, our business, financial condition, results of operations or cash flow could be affected materially and adversely. In that case, you could lose all or part of your investment in our common stock.

Risks Related to the Pending Acquisition

We may not consummate the Pending Acquisition, and the closing of this offering is not conditioned on its consummation.

We intend to use the net proceeds from this offering to fund a portion of the purchase price of the Pending Acquisition described above under “Summary—Recent Developments—Pending Acquisition.” However, the closing of this offering is not conditioned on the consummation of the Pending Acquisition. There can be no assurances that the Pending Acquisition will be consummated on the terms described herein or at all, or that the consummation of the Pending Acquisition will not be delayed beyond the expected closing date. If we do not complete the Pending Acquisition, we will not have the opportunity to attempt to realize the benefits we believe the acquisition will afford us.

We have performed only a limited investigation of the ExL Properties. The completion of the Pending Acquisition is subject to specified closing conditions and to the right of one or both of the parties to terminate the transaction including in the event that more than specified adjustments to the purchase price are required. If one or more of the closing conditions are not satisfied, or if the transaction is otherwise terminated, the Pending Acquisition may not be completed. Some of these conditions are beyond our control, and we may elect not to take actions necessary to satisfy these conditions or to ensure that the transaction is not otherwise terminated.

Because the closing of this offering is not conditioned on the consummation the Pending Acquisition, if you decide to purchase shares in this offering, you should be willing to do so whether or not we complete the Pending Acquisition. If the Pending Acquisition is not consummated, our management will have broad discretion in the application of the net proceeds of this offering and could apply the proceeds in ways that you or other shareholders may not approve, which could also adversely affect the market price of our common stock. In addition, such application may not be as beneficial to us as the Pending Acquisition may have been. If the Pending Acquisition is delayed, not consummated or consummated on terms different from those described herein, the market price of our common stock may decline. Further, a failed transaction may result in negative publicity or a negative impression of us in the investment community and may affect our relationships with our business partners. In addition, pending the potential use of the proceeds of this offering to fund a portion of the purchase price for the Pending Acquisition, we intend to use the proceeds of this offering to repay

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borrowings under our revolving credit facility. Our management will have broad discretion with respect to the use of future drawdowns on our revolving credit facility and may use these funds in ways that you or other shareholders may not support, which could adversely affect the market price of our common stock. Please see “Use of Proceeds.”

The Pending Acquisition is not conditioned upon our receipt of any financing, and there can be no assurance that we will obtain the funds necessary to complete the Pending Acquisition on acceptable terms or at all. This offering is not conditioned upon the completion of any other financing to complete the Pending Acquisition, and completion of this offering will not provide us with all of the financing necessary to complete the Pending Acquisition. Failure to complete the Pending Acquisition could cause us to be in breach of the ExL Purchase Agreement, could result in our loss of our performance deposit paid upon execution of such agreement, litigation and other losses to us, and a decline in the market price of our common stock.

We may not be able to achieve the expected benefits of the Pending Acquisition and may have difficulty integrating with the Pending Acquisition.

Even if we consummate the Pending Acquisition, we may not be able to achieve the expected benefits of the Pending Acquisition. There can be no assurance that the Pending Acquisition will be beneficial to us. We may not be able to integrate and develop the ExL Properties without increases in costs, losses in revenues or other difficulties. Any unexpected costs or delays incurred in connection with the integration and development of the ExL Properties could have an adverse effect on our business, results of operations, financial condition and prospects, as well as the market price of our common stock.

Our assessment of ExL Properties to date has been limited and, even by the time of closing, it will not reveal all existing or potential problems, nor will it permit us to become familiar enough with the properties to assess fully their capabilities and deficiencies. In the course of our assessment, we will not receive an independent reserve engineer report related to the ExL Properties. We may incur costs or experience problems related to the ExL Properties in the Pending Acquisition, and we may not have adequate recourse against ExL. Although we will inspect the properties being sold to us, inspections may not reveal all title, structural or environmental problems. We may be required to assume the risk of the physical condition of the properties in addition to the risk that the properties may not perform in accordance with our expectations. Our ability to make specified claims against ExL in the Pending Acquisition generally expires over time and we may be left with no recourse for liabilities and other problems associated with the Pending Acquisition that we do not discover prior to the expiration date related to such matters under the ExL Purchase Agreement.

The market price of our common stock may decline as a result of the Pending Acquisition if, among other things, the integration and development of the ExL Properties is unsuccessful or if the liabilities, expenses, title, environmental and other defects, or transaction costs related to the Pending Acquisition are greater than expected or the ExL Properties do not yield the anticipated returns. The market price of our common stock may decline if we do not achieve the perceived benefits of the Pending Acquisition as rapidly or to the extent anticipated by us or by securities market participants or if the effect of the Pending Acquisition, including the obligations incurred to finance the Pending Acquisition, on our business results of operations or financial condition or prospects is not consistent with our expectations or those of securities market participants.

Upon consummation of the Pending Acquisition, our overall level of debt and preferred stock obligations will increase, which could adversely affect us.

Upon consummation of the Pending Acquisition, our overall debt level will increase from approximately $1.4 billion at March 31, 2017 to approximately $1.6 billion at such date on a pro forma

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basis after giving effect to such Pending Acquisition and our senior notes offering. In connection with the Pending Acquisition, we will issue preferred stock with an aggregate initial liquidation preference of $250.0 million that requires us, upon request of holders of a majority of the then-outstanding shares of preferred stock, to redeem the preferred stock, in whole or in part, on or after the seventh anniversary of its issuance and upon certain defaults and changes of control. After the completion of the Pending Acquisition, our level of debt and other obligations could have significant adverse consequences on our business and future prospects, including the following:

Risk Related to Our Sale of Assets

We may not complete or recognize the anticipated benefits from the sale of our non-core assets.

We have recently begun efforts to sell our assets in the Marcellus and the Utica and also expect to begin efforts in the near term for the sale of other non-core assets in our portfolio. There can be no assurance that we will be able to sell any of these assets on our desired time frame on acceptable terms, including our desired price, or at all. Our sales processes for some of these assets are in their beginning stages, and we have no agreements in place to sell any of these assets. Our targeted gross proceeds are subject to numerous uncertainties inherent in the sale of oil and gas properties, most of which are beyond our control including oil prices and buyers’ expectations regarding future oil prices, reserve estimates and costs to produce such reserves. The timing of any sale is inherently uncertain and beyond our control. Any divestiture or disposition could expose us to significant risks, including, without limitation, costly fees for legal and transaction-related services, diversion of management resources, loss of key personnel and reduction in revenue. Further, we may be required to retain or indemnify the buyer against certain liabilities and obligations in connection with any such divestiture or disposition, and we may also become subject to third-party claims arising out of such divestiture or disposition. We may not be successful in overcoming these risks or any other problems encountered in connection with these divestures that may adversely affect our business, financial position and operating results.

Risks Related to the Common Stock

Our issuance of common stock, preferred stock and warrants could trigger a limitation on our ability to utilize net operating loss carryforwards.

Our ability to utilize U.S. net operating loss carryforwards to reduce future taxable income is subject to various limitations under the Internal Revenue Code of 1986, as amended (the “Code”). The utilization of such carryforwards may be limited under Section 382 of the Code upon the occurrence of certain ownership changes resulting from the sale or exchange of our stock by shareholders and our offering of stock (including certain preferred stock, such as the preferred stock to be issued in connection with the Pending Acquisition, and including warrants) if during any three-year period there is an aggregate change of more than 50% in the beneficial ownership of our stock. In the event of such

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an ownership change, Section 382 of the Code imposes an annual limitation on the amount of our taxable income that can be offset by these loss carryforwards. The limitation is generally equal to the product of (a) the fair market value of our equity multiplied by (b) a percentage approximately equivalent to the yield on long-term tax exempt bonds during the month in which an ownership change occurs. In addition, the limitation is increased if there are recognized built-in gains during any post-change year, but only to the extent of any net unrealized built-in gains inherent in the assets sold. Our issuance of common stock pursuant to this offering and our issuance of preferred stock and warrants could, taken together with other transactions with respect to our stock, trigger an ownership change under Section 382 of the Code and therefore a limitation on our ability to utilize our U.S. loss carryforwards. Any such limitation could cause some of our loss carryforwards to expire before we would be able to utilize them to reduce taxable income in future periods, possibly resulting in a substantial income tax expense or write down of our tax assets or both.

If the preferred stock and warrants issuance is consummated, a substantial number of shares of our common stock may be issued upon the redemption of the preferred stock with common stock, the payment of common stock as dividends or exercise of the warrants, which issuances may dilute the ownership interests of existing shareholders, or may otherwise reduce the value of our common stock.

If we complete the preferred stock and warrants issuance, the issuance of common stock in respect of such instruments will dilute the ownership interests and voting power of existing shareholders. We may choose to, or be required to, deliver shares of our common stock in satisfaction of the quarterly dividend, and at our election we may issue common stock upon certain redemptions of any such preferred stock. All of those issuances will value the common stock at a discount to a market price valuation during a measurement period near the time of issuance. Additionally, at the closing of the preferred stock and warrants issuance, we will issue 2,750,000 warrants. The warrants are required to be exercised on a cashless “net” exercise basis. Any sales, or expectation of sales, in the public market of shares of our common stock issuable in respect of the preferred stock or warrants could adversely affect prevailing market prices of our common stock.

Holders of the preferred stock have rights that may restrict the ability of the Company to operate its business or be adverse to holders of common stock.

If we complete the preferred stock issuance, the Statement of Resolutions under which the preferred stock would be issued will contain covenants that, among other things, so long as the certain funds managed or sub-advised by GSO Capital Partners LP and its affiliates beneficially own more than 50% of the outstanding preferred stock, limit the Company’s ability to, without the written consent of a designated representative of the preferred stock: (i) issue stock senior to or on parity with the preferred stock, (ii) incur indebtedness that would cause us to exceed a specified leverage ratio, (iii) amend, modify, alter or supplement our articles of incorporation or the Statement of Resolutions in a manner that would adversely affect the rights, preferences or privileges of the preferred stock, (iv) enter into or amend certain debt agreements that would be more restrictive on the payment of dividends on, or redemption of, the preferred stock than those existing on the preferred stock closing and (v) pay distributions on, purchase or redeem our common stock or other stock junior to the preferred stock that would cause us to exceed a specified leverage ratio. We can be required to redeem the preferred stock (i) after the seventh anniversary of its initial issuance or (ii) at any time we fail to pay a dividend, subject to limited cure rights.

Holders of the preferred stock will have additional rights in the event the Company fails to timely pay dividends, fails to redeem the preferred stock upon a change of control if required or fails to redeem the preferred stock upon request of the holders of preferred stock following the seventh anniversary of the date of issuing the preferred stock. These rights include (i) that holders of a majority

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of the then-outstanding preferred stock will have the exclusive right, voting separately as a class, to appoint and elect up to two directors to the Company’s board of directors; (ii) that approval of the holders of a majority of the then-outstanding preferred stock will be required prior to incurring indebtedness subject to a leverage ratio, declaring or paying prohibited distributions or issuing equity of subsidiaries to third parties; and (iii) that holders of a majority of the then-outstanding preferred stock will have the right to increase dividend payments and the ability to require us to pay dividends in common stock.

Holders of the preferred stock will also have limited voting rights with respect to potential amendments to the Company’s articles of incorporation or the Statement of Resolutions that have an adverse effect on the existing terms of the preferred stock and in certain other limited circumstances or as required by law. See “Preferred Stock and Warrants Issuance” for additional information regarding our preferred stock.

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USE OF PROCEEDS

We expect to receive net proceeds from this offering of 15,600,000 shares of common stock offered by this prospectus, before paying offering expenses, of approximately $222.8 million. We intend to use the net proceeds from this offering to fund a portion of the purchase price for the Pending Acquisition and for general corporate purposes. Pending the closing of the Pending Acquisition, we intend to use the net proceeds from this offering to reduce borrowings under our revolving credit facility, including to repay the borrowings used for the $75.0 million deposit on the purchase price for the Pending Acquisition. We intend to use net proceeds not used to pay the purchase price for the Pending Acquisition, including in the event we do not consummate the Pending Acquisition, for general corporate purposes, including to fund future potential acquisitions or a portion of our 2017 and 2018 capital expenditure plans. Please see “Summary—Recent Developments—Pending Acquisition” and “Risk Factors—Risks Related to the Pending Acquisition.”

As of March 31, 2017, we had $123.0 million of borrowings outstanding under our revolving credit facility and $0.4 million in letters of credit, which reduce the amounts available under our revolving credit facility. Our revolving credit facility matures on May 4, 2022 as a result of the ninth amendment to the revolving credit agreement that was entered into on May 4, 2017. As of June 22, 2017, we had $196.5 million of borrowings outstanding under our revolving credit facility with a weighted average interest rate of 3.20% and $0.4 million in letters of credit outstanding. The borrowings reflected do not include subsequent borrowings to fund the purchase price deposit for the Pending Acquisition or pay a financing commitment fee for the issuance of preferred stock. Borrowings under our revolving credit facility were used to fund our capital expenditure program and to pay the purchase price deposit for the Pending Acquisition. Affiliates of the underwriters are lenders under our revolving credit facility and, as a result, may receive a portion of the net proceeds of this offering. Because affiliates of certain of the underwriters may receive more than 5% of the net proceeds in this offering, such underwriters are deemed to have a “conflict of interest” under FINRA Rule 5121. Accordingly, this offering is being conducted in accordance with FINRA Rule 5121. For more information, see “Underwriting (Conflicts of Interest)—Conflicts of Interest.”

Neither the completion of this offering, our senior notes offering or the Pending Acquisition is contingent upon the completion of the other. This offering is not contingent upon the senior notes offering, and those senior notes are required to be redeemed in the event the Pending Acquisition does not occur by a specified date. This offering is not contingent upon the preferred stock and warrants issuance although that issuance is contingent upon the completion of this offering, the senior notes offering and the Pending Acquisition. As a result, it is possible that this offering occurs and some or all of the other transactions do not occur.

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CAPITALIZATION

The following table sets forth our unaudited cash and capitalization as of March 31, 2017:

You should read this table in conjunction with our consolidated financial statements and related notes and the sections entitled “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included in our annual report on Form 10-K for the year ended December 31, 2016 and our Quarterly Report on Form 10-Q for the quarter ended March 31, 2017, each of which is incorporated by reference in this prospectus supplement, as well as the sections of this prospectus supplement entitled “Summary—Recent Developments” and “Unaudited Pro Forma Condensed Combined Financial Information.”

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UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION

On June 28, 2017, we and our wholly-owned subsidiary Carrizo (Permian) LLC entered into the ExL Purchase Agreement with ExL to acquire the ExL Properties.

The following unaudited pro forma condensed combined financial information is presented to illustrate the effect of the Pending Acquisition on our historical financial position and results of operations. The unaudited pro forma condensed combined balance sheet as of March 31, 2017 is based on the historical consolidated balance sheet as of March 31, 2017 adjusted to give effect as if the Pending Acquisition occurred on March 31, 2017. The unaudited pro forma condensed combined statements of operations for the three months ended March 31, 2017 and the year ended December 31, 2016 are based on the historical consolidated statements of operations for such periods adjusted to give effect to the Pending Acquisition as if it had occurred on January 1, 2016. The unaudited pro forma condensed combined financial information should be read in conjunction with our consolidated financial statements and related notes included in our Annual Report on Form 10-K for the year ended December 31, 2016 and our Quarterly Report on Form 10-Q for the quarter ended March 31, 2017, each of which is incorporated by reference into this prospectus supplement, and the audited combined statements of revenues and direct operating expenses of ExL included in this prospectus supplement.

The pro forma condensed combined financial information is unaudited and presented for illustrative purposes only and does not purport to represent what the statements of operations would have been had the Pending Acquisition occurred on January 1, 2016, nor is it indicative of our future operating results.

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CARRIZO OIL & GAS, INC.

UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET

(in thousands, except per share amounts)

See the accompanying notes to the unaudited pro forma condensed combined financial statements.

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CARRIZO OIL & GAS, INC.

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

(in thousands, except per share amounts)

See the accompanying notes to the unaudited pro forma condensed combined financial statements.

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CARRIZO OIL & GAS, INC.

UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENT OF OPERATIONS

(in thousands, except per share amounts)

See the accompanying notes to the unaudited pro forma condensed combined financial statements.

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CARRIZO OIL & GAS, INC.

NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS

1. BASIS OF PRESENTATION

On June 28, 2017, Carrizo Oil & Gas, Inc. and its wholly-owned subsidiary, Carrizo (Permian) LLC (the “Company”) entered into a purchase and sale agreement (the “ExL Purchase Agreement”) with ExL Petroleum Management, LLC and ExL Petroleum Operating Inc. (together, “ExL”) to acquire approximately 16,488 net acres located in the Delaware Basin in Reeves and Ward Counties, Texas (the “ExL Properties”) for a purchase price of $648.0 million, subject to customary purchase price adjustments (the “ExL Acquisition”). In addition, the Company has agreed to make a contingent payment of $50.0 million per year if the average daily closing spot price of a barrel of West Texas Intermediate crude oil as measured by the U.S. Energy Information Administration (“WTI Average Price”) is above $50.00/Bbl for any of the years of 2018, 2019, 2020 and 2021 (the “Contingent Payment”). The Contingent Payment will be zero for the respective year if the WTI Average Price of a barrel of oil is below $50.00/Bbl for any of such years, and the Contingent Payment is capped at and will not exceed $125.0 million. Upon execution of the ExL Purchase Agreement, we paid $75.0 million as a performance deposit for our obligations under that agreement with the remaining purchase price due at closing. The Company currently expects the ExL Acquisition to close in mid-August 2017, subject to satisfaction of specified closing conditions. The ExL Acquisition has an effective date of May 1, 2017. The ExL Acquisition will be funded with net proceeds from the financing transactions described below.

The following unaudited pro forma condensed combined financial information is presented to illustrate the effect of the ExL Acquisition on the Company’s historical financial position and results of operations. The unaudited pro forma condensed combined balance sheet as of March 31, 2017 is based on the historical consolidated balance sheet as of March 31, 2017 adjusted to give effect as if the ExL Acquisition occurred on March 31, 2017. The unaudited pro forma condensed combined statements of operations for the three months ended March 31, 2017 and the year ended December 31, 2016 are based on the historical consolidated statements of operations for such periods adjusted to give effect to the ExL Acquisition as if it had occurred on January 1, 2016. The unaudited pro forma condensed combined financial information should be read in conjunction with the Company’s historical consolidated financial statements and notes thereto contained in the Company’s 2016 Annual Report on Form 10-K, filed on February 27, 2017, and its quarterly report on Form 10-Q filed on May 9, 2017, and the audited combined statements of revenues and direct operating expenses of ExL filed herewith.

The unaudited pro forma condensed combined financial statements give effect to the transactions described below. Each of the financing transactions includes any discounts, commissions and commitment fees.

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CARRIZO OIL & GAS, INC.

NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS—Continued

The unaudited pro forma condensed combined balance sheet is based on the preliminary allocation of the purchase price before purchase price adjustments which will relate to the revenues, operating expenses and capital expenditures from the effective date to the closing date. As a result, the final purchase price may be different than the preliminary purchase price.

The unaudited pro forma condensed combined financial information does not purport to represent what the statements of operations would have been had the ExL Acquisition occurred on January 1, 2016, nor is it indicative of the Company’s future operating results. The Company’s management believes the assumptions used provide a reasonable basis for presenting the significant effects directly attributable to the ExL Acquisition.

2. UNAUDITED PRO FORMA CONDENSED COMBINED BALANCE SHEET

The unaudited pro forma condensed combined balance sheet as of March 31, 2017 reflects the following pro forma adjustments:

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CARRIZO OIL & GAS, INC.

NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS—Continued

The current preliminary purchase price allocation is based on a preliminary discounted cash flow analysis. The purchase price allocation for the ExL Acquisition is subject to change based on future commodity prices on the closing date as well as purchase price adjustments, which will primarily relate to the revenues, operating expenses and capital expenditures from the May 1, 2017 effective date to the closing date. The preliminary allocation of the purchase price is presented below:

3. UNAUDITED PRO FORMA CONDENSED COMBINED STATEMENTS OF OPERATIONS

The unaudited pro forma condensed combined statements of operations for the three months ended March 31, 2017 and the year ended December 31, 2016 reflect the following pro forma adjustments:

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CARRIZO OIL & GAS, INC.

NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS—Continued

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PREFERRED STOCK AND WARRANTS ISSUANCE

On June 28, 2017, we entered into a purchase agreement with the GSO Funds to issue and sell in a private placement (i) 250,000 shares of the preferred stock and (ii) warrants for 2,750,000 shares of our common stock, with an exercise price of $16.08 per share, exercisable only on a net share settlement basis for a cash purchase price equal to $970 per share of preferred stock purchased.

The preferred stock will initially have a liquidation preference of $1,000 (the “liquidation preference”). The holders of preferred stock will be entitled to receive in cash quarterly cumulative dividends at an annual rate of 8.875% of the liquidation preference per share. We may, however, at our election, pay all or a portion of the preferred stock dividends by delivering a number of shares of our common stock equal to the dividend amount divided by 97% of the trailing five-trading-day volume weighted average price (“VWAP”) per common stock share as follows: (i) with respect to any dividend declared in respect of a quarter ending on December 15, 2017 and on or prior to September 15, 2018, up to 100% of the dividend; (ii) with respect to any dividend declared in respect of a quarter ending on December 15, 2018 and on or prior to September 15, 2019, up to 75% of the dividend; or (iii) with respect to any dividend declared in respect of a quarter ending on December 15, 2019 and on or prior to September 15, 2020, up to 50% of the dividend. If we fail to satisfy the preferred stock dividend on the applicable dividend payment date, then the unpaid dividend will be added to the liquidation preference until paid. If we fail to pay the quarterly dividend on the applicable dividend payment date and such failure continues for three months past the applicable payment date, then the holders of the preferred stock will be entitled to additional rights, as described below.

On or prior to the third anniversary of the closing date for the preferred stock and warrants issuance (the “preferred stock closing”), we may redeem all or a portion of the outstanding shares of preferred stock at 104.4375% of the original $1,000 liquidation preference plus a make-whole premium of the preferred stock dividends (other than currently accrued and unpaid dividends) payable from the date of redemption through the third anniversary of the preferred stock closing, plus accrued and unpaid dividends. After the third anniversary of the preferred stock closing, we may redeem all or a portion of the outstanding shares of preferred stock at redemption prices decreasing from 104.4375% of the original $1,000 liquidation preference to the original $1,000 liquidation preference after the fifth anniversary of the preferred stock closing, plus accrued and unpaid dividends. We refer to the redemption prices in the prior two sentences as the “company redemption price.” We may at any time on or before the first anniversary of the preferred stock closing, subject to certain conditions, redeem up to 50,000 shares of preferred stock at a redemption price equal to the liquidation preference, which includes accrued and unpaid dividends, with the proceeds of sales of certain oil and gas properties, the sale or issuance of our common stock and the sale of any of our wholly owned subsidiaries after the closing date.

On or after the seventh anniversary of the preferred stock closing, or at any time if we fail to pay a quarterly dividend and such failure is not cured within three months, a designated representative of the preferred stock (the “holder representative”), on behalf of the holders of preferred stock, may elect to have us redeem all or a portion of the preferred stock at the then-applicable company redemption price. We may elect to satisfy any such redemption elected by the preferred stock holders by delivering cash, shares of common stock or a combination thereof. The number of shares of common stock to be delivered in the redemption, if applicable, will be determined using a price per share equal to 90% of the trailing 10-trading-day VWAP per common stock share. In the event we elect to settle the redemption called by the holder representative in common stock, the holder representative, in its sole discretion on behalf of the holders of preferred stock, may elect to revoke its redemption notice or reduce the number of shares to be redeemed.

If a change of control (as defined in the Statement of Resolutions governing the preferred stock) occurs, we may be required by the holders of the preferred stock to redeem the preferred stock for cash at the company redemption price if we do not afford the holders of the preferred stock an election to be

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redeemed in cash at a price equal to $1,010 per share plus accrued and unpaid dividends or to retain the preferred stock, which may be in the form of a substantially equivalent security in the surviving or successor entity. We may also make alternative arrangements with the preferred stock holders. However, any such redemption in cash will be tolled until a date that will not result in the preferred stock being characterized as “disqualified stock” or similar concepts under our debt instruments.

So long as the GSO Funds and their affiliates beneficially own more than 50% of the outstanding shares of preferred stock, the preferred stock will be subject to certain restrictions that limit our ability to (i) issue stock senior to or on a parity with the preferred stock, (ii) incur indebtedness that would cause us to exceed a specified leverage ratio, (iii) amend, modify, alter or supplement our articles of incorporation or the Statement of Resolutions in a manner that would adversely affect the rights, preferences or privileges of the preferred stock, (iv) enter into or amend certain debt agreements that would be more restrictive on the payment of dividends on, or redemption of, the preferred stock than those existing on the preferred stock closing and (v) pay distributions on, purchase or redeem our common stock or other stock junior to the preferred stock that would cause us to exceed a specified leverage ratio. In addition, in certain circumstances, if we fail to redeem the preferred stock or pay dividends, the holders will be entitled to additional rights, including an increased dividend rate, the right to require us to pay preferred stock dividends in common stock at a price per share of 95% of the trailing five-trading-day VWAP per common stock share, the right to appoint up to two directors to our board of directors and the right to approve incurring indebtedness subject to a leverage ratio, declaring or paying certain prohibited distributions or issuing equity of subsidiaries to third parties.

In connection with the preferred stock closing, we will issue to the GSO Funds warrants to purchase 2,750,000 shares of common stock at an exercise price of $16.08, subject to adjustment. The warrants will be exercisable for a ten-year period. The warrants may only be exercised on a cashless net exercise basis and are subject to customary anti-dilution adjustments.

We also agreed to enter into a registration rights agreement with the GSO Funds on the preferred stock closing, pursuant to which we will agree to provide certain registration and other rights for the benefit of the GSO Funds. In addition, we also agreed to enter into a standstill and voting agreement with the GSO Funds, pursuant to which the GSO Funds will agree to refrain from taking certain corporate actions regarding us and agree to vote their common stock at the GSO Funds’ election either pro rata with other shareholders or as recommended by our board.

We expect to receive net proceeds of approximately $242.5 million from the preferred stock and warrants issuance (prior to payment of commitment fees and expenses of the issuance) at the preferred stock closing, subject to certain closing conditions, including completion of the Pending Acquisition. The net proceeds from the preferred stock and warrants issuance are expected to be used to finance a portion of the purchase price for the Pending Acquisition that is due at closing. This offering is not contingent on the preferred stock and warrants issuance although that issuance is contingent upon the completion of this offering, the senior notes offering and the Pending Acquisition. The foregoing description and any other information regarding the preferred stock and warrants issuance are included herein solely for informational purposes. This prospectus supplement and any related communication shall not be deemed an offer to sell or a solicitation to buy any securities that may be offered in the preferred stock and warrants issuance.

The foregoing description of the preferred stock and warrants issuance and the related documentation does not purport to be complete and is qualified in its entirety by reference to the full text of the purchase agreement, which has been filed as an exhibit to our Current Report on Form 8-K filed on June 28, 2017 and incorporated by reference herein, and the Form of Statement of Resolutions, the Form of Registration Rights Agreement, the Form of Warrant Agreement and the Form of Standstill and Voting Agreement attached to the purchase agreement, which are exhibits to the purchase agreement.

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PRICE RANGE OF COMMON STOCK

On June 28, 2017, we had 65,835,820 shares of common stock outstanding, held of record by approximately 85 record holders. Our common stock, par value $0.01 per share, trades on the NASDAQ Global Select Market under the symbol “CRZO.”

The closing price of our common stock on June 28, 2017 as reported on the NASDAQ Global Select Market was $15.61 per share. The following table shows the high and low sales prices per share of our common stock on the NASDAQ Global Select Market for the periods indicated.