FIRST AMENDMENT

FIRST AMENDMENT, dated as of August 17, 2005 (this “Amendment”), to the Credit Agreement, dated as of July 29, 2004 (the “Credit Agreement”), among Burlington Resources Inc., a Delaware corporation (“Parent” or the “US Facility Borrower”), Burlington Resources Canada Ltd., an Alberta corporation (“BRCL”), Burlington Resources Canada (Hunter) Ltd., an Alberta corporation (“Canadian Hunter” and, together with BRCL, the “Canadian Borrowers”, and, together with Parent as a borrower under the Canadian Facility, the “Canadian Facility Borrowers”; the Canadian Facility Borrowers, together with the US Facility Borrower, the “Borrowers”), the lenders party thereto (the “Existing Lenders”), JPMorgan Chase Bank, N.A., Toronto Branch, as Canadian Swing Line Lender and a Canadian L/C Issuer, and JPMorgan Chase Bank, N.A., as Administrative Agent, US Swing Line Lender and a US L/C Issuer.

RECITALS

WHEREAS, the Borrowers, the Existing Lenders and the Administrative Agent are parties to the Credit Agreement;

WHEREAS, the Borrowers have requested that the Existing Lenders and the Administrative Agent agree to amend certain provisions of the Credit Agreement, and that the New Lenders (as defined below) become parties to the Credit Agreement, in each case as set forth herein, and the Existing Lenders, the New Lenders and the Administrative Agent are agreeable to such request upon the terms and subject to the conditions set forth herein;

NOW, THEREFORE, in consideration of the premises and mutual agreements contained herein, and for other valuable consideration the receipt of which is hereby acknowledged, the Borrowers, the Existing Lenders, the New Lenders and the Administrative Agent hereby agree as follows:

AGREEMENT

Section 1. Definitions. Unless otherwise defined herein, terms defined in the Credit Agreement and used herein shall have the meanings given to them in the Credit Agreement.

Section 2. Amendments. The parties hereto hereby agree that on and as of the First Amendment Effective Date (as defined below), the Credit Agreement shall be amended as follows:

(a) Amendment to Section 1.01 (Defined Terms). Section 1.01 of the Credit Agreement shall be amended by deleting the definition “Maturity Date” in its entirety and inserting in lieu thereof the following:

““Maturity Date” means the later of (a) August 17, 2010, and (b) if maturity is extended pursuant to Section 4.07, such extended maturity date as determined pursuant to Section 4.07 (it being understood and agreed that any such maturity shall not be deemed extended for any Lender that has not consented to such extension).”

The foregoing amendment to the definition of Maturity Date shall not be deemed to constitute a request to extend the Maturity Date pursuant to Section 4.07(a) of the Credit Agreement, and the US Facility Borrower may request, for itself and the Canadian Borrowers, up to two such extensions in the future in accordance with the terms and conditions set forth in Section 4.07 of the Credit Agreement.

(b) Amendment to Section 4.02 (Fees). Section 4.02(b)(i) of the Credit Agreement shall be amended by deleting the words “12.5 Basis Points” and inserting in lieu thereof “10.0 Basis Points”.

(c) Amendment to Schedule 1.01 (Pricing Grid). Schedule 1.01 to the Credit Agreement shall be amended by deleting such Schedule 1.01 in its entirety and replacing it with the Schedule 1.01 attached hereto.

Section 3. Commitments. (a) As of the First Amendment Effective Date, the Canadian Commitments and the US Commitments shall be as set forth in Schedule 2.01 attached hereto, and Schedule 2.01 to the Credit Agreement is hereby amended by deleting such Schedule 2.01 in its entirety and replacing it with the Schedule 2.01 attached hereto.

(b) From and after the First Amendment Effective Date, (i) each Person indicated as having a Commitment pursuant to Schedule 2.01 attached hereto that is not an Existing Lender (each such Person, a “New Lender”) shall be deemed to be a party to the Credit Agreement and shall have the rights and obligations of a Lender (and, as applicable, a US Lender and/or a Canadian Lender) thereunder, and (ii) each Existing Lender that is not indicated as having a Commitment pursuant to Schedule 2.01 hereto (each such Existing Lender, a “Departing Lender”) shall relinquish its rights and be released from its obligations under the Credit Agreement and shall cease to be a party to the Credit Agreement, provided, however, that each Departing Lender shall retain any claim with respect to any fee, interest, cost, expense or indemnity that accrues, or relates to an event that occurs, prior to the First Amendment Effective Date pursuant to Section 2.04(i), 2.04(j), 3.04(i), 3.04(j), 4.01, 4.02, 5.01, 5.04, 5.05 or 12.04 of the Credit Agreement, in each case as in effect immediately prior to the First Amendment Effective Date.

Section 4. Representations; No Default. Each of the Borrowers hereby represents and warrants to the Existing Lenders (other than the Departing Lenders), the New Lenders and the Administrative Agent that (a) this Amendment has been duly executed and delivered by such Borrower and constitutes its legal, valid and binding obligation, enforceable against it in accordance with its terms, (b) no Loan or Letter of Credit is or will be outstanding at any time on and after the date hereof and prior to the First Amendment Effective Date, and (c) on and as of the First Amendment Effective Date, and after giving effect to this Amendment, (i) each representation and warranty contained in Section 7.01 of the Credit Agreement is true and correct in all material respects as though made on and as of such date (or, if such representation and warranty is stated to be made as at a specific date or for a specific period, as at the original specified date or with respect to the original specified period), (ii) no Default has occurred and is continuing and (iii) from the date of the most recent financial statements of Parent delivered pursuant to Section 8.03 of the Credit Agreement to and including the First Amendment Effective Date there has been no material adverse change in the consolidated financial condition, or in the consolidated results of operations, of Parent and its consolidated Subsidiaries from that shown on such most recent financial statements.

Section 5. Fees. (a) The Borrowers agree to pay to each Existing Lender (other than any Existing Lender that is a Departing Lender) and each New Lender that, in each case, executes and delivers a copy of this Amendment to the Administrative Agent (or its counsel) at or prior to 12:00 (noon), New York City time, on August 17, 2005, through the Administrative Agent, an amendment fee (collectively, the “Amendment Fees”) in an amount equal to 2.0 Basis Points of the Commitment of such Person on the First Amendment Effective Date, as set forth on Schedule 2.01 hereto. The Amendment Fees shall be payable in full, in immediately available funds, on the First Amendment Effective Date. Once paid, none of such fees shall be refundable under any circumstances.

(b) On the First Amendment Effective Date, the Borrowers shall pay to each Departing Lender, through the Administrative Agent, any and all Facility Fees and other fees under the Credit Agreement accrued for the account of such Departing Lender as of such date and not yet paid.

Section 6. Conditions to Effectiveness. This Amendment shall not become effective until the date (the “First Amendment Effective Date”) on which (a) the Administrative Agent shall have received (i) counterparts of this Amendment, duly executed and delivered by a duly authorized officer of each of the Borrowers, the Administrative Agent, each of the Existing Lenders and each of the New Lenders and (ii) a certificate of each Borrower dated as of the First Amendment Effective Date signed by a Responsible Officer of such Borrower, certifying that the warranties and representations contained in Section 4 hereof are true and correct as of the First Amendment Effective Date and (b) the Administrative Agent and the Joint Lead Arrangers shall have received all fees and other amounts due and payable to them on or prior to the First Amendment Effective Date, including, to the extent invoiced, payment or reimbursement of the Administrative Agent’s reasonable out-of-pocket expenses in connection with this Amendment and any other out-of-pocket expenses of the Administrative Agent required to be paid or reimbursed pursuant to the Credit Agreement, including the reasonable fees, charges and disbursements of counsel for the Administrative Agent.

Section 7. Effect of Amendment. Except as expressly set forth herein, this Amendment shall not be deemed to be a modification or amendment of any other term, condition, obligation, covenant or agreement contained in the Credit Agreement or any other provision of the Credit Agreement, all of which are ratified and affirmed in all respects and shall continue in full force and effect. In furtherance of the foregoing, it is expressly agreed that all interest and fees accruing under the Credit Agreement in respect of periods prior to the First Amendment Effective Date will accrue at the rates specified in the Credit Agreement prior to its amendment hereby. On and after the First Amendment Effective Date, each reference in the Credit Agreement to “this Agreement”, “hereunder”, “hereof”, “herein” or words of like import shall be deemed a reference to the Credit Agreement as amended hereby.

Section 8. General.

(a) Governing Law. This Amendment shall be governed by, and construed and interpreted in accordance with, the laws of the State of New York.

(b) Costs and Expenses. The Borrowers agree to reimburse the Administrative Agent for its reasonable out-of-pocket expenses in connection with this Amendment, including the reasonable fees, charges and disbursements of counsel for the Administrative Agent.

(c) Counterparts. This Amendment may be executed by one or more of the parties hereto in any number of separate counterparts and all of said counterparts taken together shall be deemed to constitute one and the same instrument. Delivery of an executed counterpart of a signature page of this Amendment by facsimile transmission shall be as effective as delivery of a manually executed counterpart hereof.

(d) Headings. The headings of this Amendment are for purposes of reference only and shall not limit or otherwise affect the meaning hereof.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed and delivered by their respective duly authorized officers as of the date first above written.

BURLINGTON RESOURCES INC.

BURLINGTON RESOURCES CANADA LTD.

BURLINGTON RESOURCES CANADA

(HUNTER) LTD.

JPMORGAN CHASE BANK, N.A., individually and as Administrative Agent, US Swing Line Lender and US L/C Issuer

JPMORGAN CHASE BANK, N.A., TORONTO BRANCH, individually and as Canadian Swing Line Lender and Canadian L/C Issuer

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BANK OF AMERICA, N.A., individually and as US L/C Issuer

BANK OF AMERICA, N.A., CANADA BRANCH, individually and as Canadian L/C Issuer

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SIGNATURE PAGE TO FIRST AMENDMENT TO BURLINGTON RESOURCES INC. CREDIT AGREEMENT DATED AS OF JULY 29, 2004