<PAGE>
                                                                    EXHIBIT 10.3


                                 AMENDMENT NO. 1


         AMENDMENT NO. 1 (this "Amendment"), dated as of May 30, 2003, to that
certain Credit Agreement, dated as of October 12, 2001 (the "Credit Agreement";
capitalized terms used herein and not defined shall have the meanings set forth
in the Credit Agreement), among DEVON ENERGY CORPORATION ("US Borrower"), DEVON
FINANCING CORPORATION, U.L.C. ("Canadian Borrower" and, together with US
Borrower, the "Borrowers"), UBS AG, STAMFORD BRANCH, as Administrative Agent
(the "Administrative Agent"), and the lenders from time to time party thereto.

                              W I T N E S S E T H:

         WHEREAS, subsection 10.1 of the Credit Agreement permits the Credit
Agreement to be amended from time to time;

         NOW, THEREFORE, in consideration of the foregoing, and for other good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

         SECTION ONE. Amendments.

         (a) Unrestricted Subsidiaries. (i) The first sentence of the definition
of "Unrestricted Subsidiary" in Section 2.1 of the Credit Agreement shall be
replaced in its entirety with the following:

                  "Unrestricted Subsidiary" means any corporation, association,
         partnership, limited liability company, joint venture, or other
         business or corporate entity, enterprise or organization (a) which is
         listed below in this definition, or (b) in which US Borrower did not
         own an interest (directly or indirectly) as of the Closing Date, which
         thereafter became a Subsidiary of US Borrower and which, within 90 days
         after becoming a Subsidiary of US Borrower, was designated as an
         Unrestricted Subsidiary by US Borrower to Administrative Agent;
         provided that (i) in the event any such Subsidiary becomes a Material
         Subsidiary at any time, such Subsidiary shall cease to be an
         Unrestricted Subsidiary at such time and shall automatically become a
         Restricted Subsidiary and (ii) US Borrower may, from time to time,
         designate any Unrestricted Subsidiary as a Restricted Subsidiary by a
         written notice to Administrative Agent signed by the Senior Vice
         President--Finance, the Senior Vice President, Corporate Finance and
         Development, the Vice President--Corporate Finance, the Treasurer or
         the Vice President--Accounting of US Borrower, which notice shall
         certify the following conditions precedent: (1) after giving effect to
         such conversion, all representations and warranties in any Loan
         Document applicable

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                                      -2-

         to such Subsidiary shall be true in all material respects on and as of
         such date as if made on and as of the date of such conversion (except
         to the extent that the facts upon which such representations are based
         have been changed by the extension of credit hereunder), and (2) after
         giving effect to such conversion, no Default or Event of Default shall
         occur solely as a result of such conversion."

                  (ii) The following additional Subsidiaries of US Borrower
         shall be designated as Unrestricted Subsidiaries in the definition of
         "Unrestricted Subsidiary":

        (147)    308819 Alberta Ltd.
        (148)    Amax Petroleum of Canada Inc.
        (149)    Anderson Exploration Inc.
        (150)    Home Oil Company Limited
        (151)    382817 Alberta Ltd.
        (152)    2861259 Canada Inc.
        (153)    Bridger Petroleum Corporation
        (154)    Devon ARL Corporation
        (155)    Home Hydrocarbons Inc.
        (156)    Home Oil Resources Ltd.
        (157)    Independent Pipe Line Company
        (158)    Numac Energy Inc.
        (159)    Plains Petroleums Limited
        (160)    Scurry Rainbow Oil (Sask) Ltd.
        (161)    The Winnipeg Western Land Corporation Limited
        (162)    Numac Energy (Cenako) Inc.
        (163)    Numac Energy (US) Inc.
        (164)    Smart On Resources Inc.
        (165)    DEC Operating, Inc.
        (166)    Devon Gas Corporation
        (167)    Devon MND Service, Inc.
        (168)    Mitchell Resorts, Inc.
        (169)    MND Exploration & Production, Inc.
        (170)    The Woodlands Venture Capital Company
        (171)    Acacia Natural Gas Corporation
        (172)    Devon Gas Operating, Inc.
        (173)    Devon Louisiana Gas Services, Inc.
        (174)    MND Gas Services L.L.C.
        (175)    Southwestern Gas Pipeline, Inc.
        (176)    Louisiana Chalk Gathering System



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        (177)    Louisiana Chalk Marketing Services
        (178)    Devon Gas Services L.P.
        (179)    Belvieu Environmental Fuels
        (180)    Gulf Coast Fractionators
        (181)    Big Sky Gas Marketing Corporation
        (182)    CJSC Tatex
        (183)    Energy Arrow Exploration, L.L.C.
        (184)    GAJH 1989 Limited Partnership
        (185)    Global Natural Resources Inc.
        (186)    Havre Pipeline Co. L.L.C.
        (187)    Indonesian Trust Asset (Held Directly in OIL)
        (188)    Lion G.P.I. Corporation
        (189)    Ocean Angola Corporation
        (190)    Ocean Angola (Ten), Ltd.
        (191)    Ocean Angola (Twenty-Four), Ltd.
        (192)    Ocean Brazil Santos Limiteda
        (193)    Ocean (CI-01) Corporation
        (194)    Ocean (CI-02) Corporation
        (195)    Ocean (CI-105), Ltd.
        (196)    Ocean (Cote d'Ivoire), Ltd.
        (197)    Ocean East Zeit Petroleum, Ltd.
        (198)    Ocean (Egypt) East Beni Suef, Ltd.
        (199)    Ocean (Egypt), Ltd.
        (200)    Ocean Energy (Argentina), Inc.
        (201)    Ocean Energy International, LLC
        (202)    Ocean Energy Limiteda
        (203)    Ocean Energy Nigeria Limited
        (204)    Ocean Energy (242) Limited
        (205)    Ocean Equatorial Guinea Corporation
        (206)    Ocean Field Services Company
        (207)    Ocean International Holdings, Ltd.
        (208)    Ocean International, Ltd.
        (209)    Ocean Khalique El Zeit, Ltd
        (210)    Ocean North Zeit Bay, Ltd.
        (211)    Ocean Offshore, Ltd.
        (212)    Ocean Pakistan, Ltd.
        (213)    Ocean Permian, LLC
        (214)    Ocean Ras Abu Darag, Ltd.
        (215)    Ocean SW Gebel El-Zeit, Ltd.
        (216)    Ocean South East July, Ltd.
        (217)    Ocean Syria (Block 26), Ltd.
        (218)    Ocean WAG Petroleum Ltd.

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                                      -4-


        (219)    Ocean Yemen Corporation
        (220)    Orion 1981 Drilling Fund Ltd. - Variable Interest
        (221)    Seagull Marketing Services, Inc.
        (222)    Seagull Pipeline & Marketing, Inc.
        (223)    Seagull Series 1995 Trust Delaware Partnership 1%
        (224)    Texneft Inc.
        (225)    Thousand Oaks Development Corp. J.V.
        (226)    DEC Capital S.A.R.L.
        (227)    DEC Second Capital S.A.R.L.
        (228)    Devon AOG Corporation
        (229)    Devon Energy Angola, Ltd.
        (230)    Devon Energy Charitable Foundation
        (231)    Devon Energy Eurasia, Ltd.
        (232)    Devon Energy West Africa, Ltd.
        (233)    Pivotal Funding Company L.P.
        (234)    Tall Grass Gas Services
        (235)    Devon Energy Ghana Holdings, Ltd.
        (236)    Devon Exploration do Brazil Ltda.
        (237)    Devon Financing Trust II
        (238)    Santa Fe Energy Trust
        (239)    SFER (Barbados) Ltd."

         (b) Section 7.1(a). Section 7.1(a) of the Credit Agreement shall be
replaced in its entirety with the following:

                  "(a) (i) with respect to Canadian Borrower, (A) its
         Obligations hereunder and (B) so long as the Devon Financing Guaranty
         is in effect, (1) the Indebtedness in respect of the Devon Financing
         Debentures and the Devon Financing Guaranty and (2) guaranties by the
         Canadian Borrower of Indebtedness of the US Borrower which is otherwise
         permitted to be incurred by the US Borrower in accordance with this
         Agreement; and

                       (ii) with respect to any Restricted Subsidiary that
         assumes the payment obligations of the Canadian Borrower under the
         Devon Financing Debentures or otherwise becomes liable for such payment
         obligations to the holders thereof, so long as such Restricted
         Subsidiary has executed and delivered to the Administrative Agent for
         the benefit of the Lender Parties a guaranty in form substantially
         similar to the Devon Financing Guaranty and only so long as such
         guaranty is in full force and effect, (A) Indebtedness in respect of
         such obligations and (B) guaranties by such Restricted Subsidiary of
         Indebtedness of the US Borrower or the Canadian Borrower which is
         otherwise permitted to be incurred by the US Borrower or the Canadian
         Borrower in accordance

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                                      -5-


         with this Agreement to the extent US Borrower is in compliance with
         Section 7.7 at the time such guaranty is delivered."

         (c) Section 7.4(a). Section 7.4(a) of the Credit Agreement shall be
replaced in its entirety with the following:

                  "(a) No Restricted Subsidiary of US Borrower will issue any
         additional shares of its capital stock, additional partnership
         interests or other securities or any options, warrants or other rights
         to acquire such additional shares, partnership interests or other
         securities except to US Borrower or another Restricted Person which is
         a wholly-owned direct or indirect Subsidiary of US Borrower unless (i)
         such securities are being issued to acquire a business, directly or
         indirectly through the use of the proceeds of such issuance, and (ii)
         such securities are convertible into the common or similar securities
         of US Borrower and/or may be redeemed in cash at the option of the
         Restricted Person that issued such securities. Notwithstanding the
         foregoing, this Section 7.4 shall not prohibit any transaction
         permitted pursuant to Section 7.4 of the Existing US Credit Facility as
         in effect on the date hereof whether or not terminated."

         (d) Section 10.20. A new Section 10.20 shall be added to the Credit
Agreement by adding the following language

                  "Section 10.20 Authorizations. Certificates and/or notices
         referred to in the definition of "Disclosure Report" and Sections
         6.2(a) and (b) hereof which may be signed by the Senior Vice President
         - Finance of US Borrower are permitted to be signed by the Senior Vice
         President - Finance, Senior Vice President - Corporate Finance and
         Development or the Vice President - Corporate Finance without violating
         any of the aforementioned requirements."

         SECTION TWO. Conditions to Effectiveness. This Amendment shall become
effective as of the date (the "Effective Date") when, and only when, the
Administrative Agent shall have received counterparts of this Amendment executed
by the Borrowers and the Required Lenders. The effectiveness of this Amendment
(other than Sections Five, Six and Seven hereof) is conditioned upon the
accuracy of the representations and warranties set forth in Section Three
hereof.

         SECTION THREE. Representations and Warranties. In order to induce the
Lenders and the Agents to enter into this Amendment, the Borrower represents and
warrants to each of the Lenders and the Agents that after giving effect to this
Amendment, and both before and after giving effect to transactions contemplated
by this Amendment

                  (a) no Default or Event of Default has occurred and is
         continuing;


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                                      -6-


                  (b) all of the representations and warranties in the Credit
         Agreement are true and complete in all material respects on and as of
         the date hereof as if made on the date hereof (or, if any such
         representation or warranty is expressly stated to have been made as of
         a specific date, as of such specific date);

                  (c) the Subsidiaries identified as "Unrestricted Subsidiaries"
         under the Credit Agreement immediately after giving effect to this
         Amendment will be identical to the list of "Unrestricted Subsidiaries"
         under the Amended and Restated US Credit Agreement dated as of June 7,
         2002, among US Borrower, Canadian Borrower, Bank of America, N.A., as
         Administrative Agent, and the lenders from time to time party thereto,
         as amended by the First Amendment thereto; and

                  (d) no Unrestricted Subsidiary is a Material Subsidiary.

         SECTION FOUR. Reference to and Effect on the Credit Agreement and the
Notes. On and after the Effective Date, each reference in the Credit Agreement
to "this Agreement," "hereunder," "hereof" or words of like import referring the
Credit Agreement, and each reference in the Notes and each of the Loan Documents
to "the Credit Agreement," "thereunder," "thereof" or words of like import
referring to the Credit Agreement, shall mean and be a reference to the Credit
Agreement, as amended by this Amendment. The Credit Agreement, the Notes and
each of the other Loan Documents, as specifically amended by this Amendment, are
and shall continue to be in full force and effect and are hereby in all respects
ratified and confirmed. The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of any Lender or any Agent under any of the Loan
Documents, nor constitute a waiver of any provision of any of the Loan
Documents.

         SECTION FIVE. Costs, Expenses and Taxes. Borrower agrees to pay all
reasonable out-of-pocket costs and expenses of the Agents in connection with the
preparation, execution and delivery of this Amendment and the other instruments
and documents to be delivered hereunder, if any (including, without limitation,
the reasonable fees and expenses of Cahill Gordon & Reindel LLP, counsel to the
Lenders) in accordance with the terms of subsection 10.4(a) of the Credit
Agreement.

         SECTION SIX. Execution in Counterparts. This Amendment may be executed
in any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which taken together shall constitute but one and the same agreement.
Delivery of an executed counterpart of a signature page to this Amendment by
telecopier shall be effective as delivery of a manually executed counterpart of
this Amendment.

         SECTION SEVEN. Governing Law. THIS AMENDMENT SHALL BE DEEMED A CONTRACT
AND INSTRUMENT MADE UNDER THE LAWS OF THE

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                                      -7-


STATE OF NEW YORK AND SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH AND
GOVERNED BY THE LAWS OF THE STATE OF NEW YORK AND THE LAWS OF THE UNITED STATES
OF AMERICA.

                            [Signature Pages Follow]


                            DEVON ENERGY CORPORATION


                            By: /s/ Brian J. Jennings
                               -------------------------------------------------
                               Name:  Brian J. Jennings
                               Title: Senior Vice President


                            DEVON FINANCING CORPORATION, U.L.C.


                            By: /s/ Brian J. Jennings
                               -------------------------------------------------
                               Name:  Brian J. Jennings
                               Title: Senior Vice President


                            UBS AG, STAMFORD BRANCH,
                            as Administrative Agent & Lender


                            By: /s/ Robert Reuter
                               -------------------------------------------------
                               Name:  Robert Reuter
                               Title: Executive Director


                            By: /s/ Lynn B. Alfarone
                               -------------------------------------------------
                               Name:  Lynn B. Alfarone
                               Title: Associate Director
                                      Banking Products Services, US


                            ABN AMRO BANK, N.V.


                            By: /s/ Frank R. Russo, Jr.
                               -------------------------------------------------
                               Name:  Frank R. Russo, Jr.
                               Title: Group Vice President


                            By: /s/ Quandra L. Kelley
                               -------------------------------------------------
                               Name:  Quandra L. Kelley
                               Title: Assistant Vice President

<PAGE>

                                      -8-


                                               BANCO ESPIRITO SANTOS, S.A.

                                               By:  /s/ Andrew M. Orsen
                                                    -----------------------
                                                    Name:  Andrew M. Orsen
                                                    Title: Vice President


                                               By:  /s/ Terry R. Hull
                                                    -----------------------
                                                    Name:  Terry R. Hull
                                                    Title: Senior Vice President



                                               BANK OF AMERICA, N.A.,
                                               as Syndication Agent and Lender


                                               By:  /s/ Richard L. Stein
                                                    ----------------------------
                                                    Name:  Richard L. Stein
                                                    Title: Principal



                                               THE BANK OF NEW YORK


                                               By:  /s/ Peter W. Keller
                                                    ----------------------------
                                                    Name:  Peter W. Keller
                                                    Title: Vice President



                                               Citibank, N.A.

                                               By:  /s/ Todd J. Mogil
                                                    ----------------------------
                                                    Name:  Todd J. Mogil
                                                    Title: Attorney-in-fact

<PAGE>

                                      -9-

                                             Credit Suisse First Boston


                                             By:  /s/ James Moran
                                                  -----------------------
                                                  Name:  James Moran
                                                  Title: Director



                                             Den norske Bank ASA


                                             By:  /s/ Nils Fykse
                                                  ----------------------------
                                                  Name:  Nils Fykse
                                                  Title: Senior Vice President


                                             By:  /s/ Stig Kristiansen
                                                  -----------------------
                                                  Name:  Stig Kristiansen
                                                  Title: Vice President



                                             DEUTSCHE BANK AG NEW YORK
                                             BRANCH


                                             By:  /s/ Philippe Sandmeier
                                                  ----------------------------
                                                  Name:  Philippe Sandmeier
                                                  Title: Director


                                             By:  /s/ Oliver Riedinger
                                                  -----------------------
                                                  Name:  Oliver Riedinger
                                                  Title: Vice President




                                             JPMorgan Chase Bank


                                             By:  /s/ Russell A. Johnson
                                                  ----------------------------
                                                  Name:  Russell A. Johnson
                                                  Title: Vice President




                                             Wachovia Bank, National Association


                                             By:  /s/ Russell Clingman
                                                  ----------------------------
                                                  Name:  Russell Clingman
                                                  Title: Director