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                                                                    EXHIBIT 10.6



                      SECOND AMENDMENT TO CREDIT AGREEMENT

         This Second Amendment to Credit Agreement (this "SECOND AMENDMENT") is
executed as of October 21, 2003 (the "EFFECTIVE DATE"), by and among Encore
Acquisition Company, a Delaware corporation ("BORROWER"). Encore Operating,
L.P., a Texas limited partnership ("OPERATING"). Fleet National Bank, a national
banking association, as Administrative Agent ("ADMINISTRATIVE AGENT"), and the
financial institutions a party hereto as Banks ("BANKS").

                              W I T N E S S E T H:

         WHEREAS, Borrower, Operating, Administrative Agent, the other Agents a
party thereto and Banks are parties to that certain Credit Agreement dated as of
June 25, 2002 (as amended, the "CREDIT AGREEMENT") (unless otherwise defined
herein, all terms used herein with their initial letter capitalized shall have
the meaning given such terms in the Credit Agreement); and

         WHEREAS, pursuant to the Credit Agreement, Banks have made a revolving
credit loan to Borrower; and

         WHEREAS, Borrower and Operating have requested that Banks (a) amend
certain terms of the Credit Agreement in certain respects, and (b) increase the
Borrowing Base to $270,000,000 to be effective as of December 1, 2003 and
continuing until the first Redetermination thereafter; and

         WHEREAS, subject to the terms and conditions set forth herein, Banks
have agreed to Borrower's and Operating's requests.

         NOW THEREFORE, for and in consideration of the mutual covenants and
agreements herein contained and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged and confessed,
Borrower, Operating, Administrative Agent and each Bank hereby agree as follows:

         SECTION 1. AMENDMENTS. In reliance on the representations, warranties,
covenants and agreements contained in this Second Amendment, and subject to the
satisfaction of the conditions precedent set forth in Section 3 hereof, the
Credit Agreement is hereby amended effective as of the Effective Date in the
manner provided in this Section 1.

         1.1.     AMENDMENT TO DEFINITIONS. The definitions of "LOAN PAPERS" and
"PERMITTED ENCUMBRANCES" contained in Section 1.1 of the Credit Agreement shall
be amended to read in full as follows:

                  "LOAN PAPERS" means this Agreement, the First Amendment, the
         Second Amendment, the Notes, the Mortgages, each Borrower Pledge
         Agreement, each Subsidiary Pledge Agreement, each Facility Guaranty,
         and all other certificates, documents or instruments delivered in
         connection with this Agreement, as the foregoing may be amended from
         time to time.

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                  "PERMITTED ENCUMBRANCES" means with respect to any asset:

                  (a)      Liens (if any) securing the Obligations (including,
         without limitation, indebtedness, liabilities and obligations pursuant
         to any Hedge Transaction entered into by a Credit Party with any Bank
         or any Affiliate of any Bank);

                  (b)      minor defects in title which do not secure the
         payment of money and otherwise have no material adverse effect on the
         value or the operation of the subject property, and for the purposes of
         this Agreement, a minor defect in title shall include, but not be
         limited to, easements, zoning restrictions, rights-of-way, servitudes,
         permits, surface leases and other similar rights in respect of surface
         operations, and easements for pipelines, streets, alleys, highways,
         telephone lines, power lines, railways and other easements and
         rights-of-way, on, over or in respect of any of the properties of any
         Credit Party that are customarily granted in the oil and gas industry;

                  (c)      contractual or statutory Liens securing obligations
         for labor, services, materials and supplies furnished to Mineral
         Interests and Liens arising under joint operating agreements entered
         into in the ordinary course of business, in each case securing
         obligations which are not delinquent (except to the extent permitted by
         Section 9.7);

                  (d)      contractual or statutory mechanic's, materialmen's,
         warehouseman's, journeyman's and carrier's Liens and other similar
         Liens arising in the ordinary course of business which are not
         delinquent (except to the extent permitted by Section 9.7);

                  (e)      Liens for Taxes or assessments not yet due or not yet
         delinquent, or, if delinquent, that are not required to be paid subject
         to satisfaction of the conditions set forth in Section 9.7;

                  (f)      lease burdens payable to third parties which are
         deducted in the calculation of discounted present value in the Reserve
         Report including, without limitation, any royalty, overriding royalty,
         net profits interest, production payment, carried interest or
         reversionary working interest;

                  (g)      Liens encumbering assets securing Debt incurred to
         finance the purchase of such assets, provided, that (i) the principal
         amount of the Debt secured by a purchased asset shall not exceed one
         hundred percent (100%) of the purchase price of such asset, (ii) such
         Liens shall not extend to or encumber any other asset of any Credit
         Party, (iii) such Liens shall attach to such purchased asset
         substantially simultaneously with the purchase of such asset, and (iv)
         the aggregate amount of all Debt secured by such Liens shall not exceed
         $15,000,000;

                  (h)      Liens securing Hedge Transactions, including, without
         limitation, pledges of cash or cash equivalents, provided, that, (i)
         such Hedge Transactions comply with Section 10.11 to the extent
         applicable, and (ii) the aggregate amount of cash or cash equivalents
         pledged (or the fair market value of other, non-cash collateral
         pledged) shall not exceed $15,000,000 at any time; and

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                  (i)      to the extent not included in clauses (a) through (h)
         above, Permitted Encumbrances under and as defined in the Mortgages.

         SECTION 2. BORROWING BASE. The Borrowing Base shall be $270,000,000
effective December 1, 2003 and continuing until the first Redetermination
thereafter. Borrower, Operating and Banks agree that the Redetermination
provided for in this Section 2 (a) shall be deemed to be the Scheduled
Redetermination to occur on December 1, 2003 pursuant to Section 5.2 of the
Credit Agreement, and (b) shall not be construed or deemed to be a Special
Redetermination for purposes of Section 5.3 of the Credit Agreement.

         SECTION 3. CONDITIONS PRECEDENT. The effectiveness of the amendments to
the Credit Agreement contained in Section 1 hereof is subject to the
satisfaction of each of the following conditions precedent:

         3.1.     NO DEFAULT. No Default or Event of Default shall have occurred
which is continuing.

         3.2.     BORROWING BASE INCREASE FEE. Borrower shall have paid to
Administrative Agent, for the ratable benefit of each Bank, a borrowing base
increase fee in an amount equal to one-quarter of one percent (0.250%) of the
amount of the increase in the Borrowing Base as reflected in Section 2 hereof.

         3.3.     OTHER FEES. Borrower shall have paid to Administrative Agent
any fees payable to Administrative Agent or any Affiliate of Administrative
Agent pursuant to this Second Amendment and any separate agreement among
Borrower, Operating, Administrative Agent or any Affiliate of Administrative
Agent in consideration for providing services in connection with the credit
facilities provided by the Credit Agreement.

         3.4.     OTHER DOCUMENTS. Administrative Agent shall have been provided
with such other documents, instruments and agreements, and Borrower and
Operating shall have taken such actions, as Administrative Agent may reasonably
require in connection with this Second Amendment and the transactions
contemplated hereby.

         SECTION 4. REPRESENTATIONS AND WARRANTIES OF BORROWER AND OPERATING. To
induce Banks and Administrative Agent to enter into this Second Amendment,
Borrower and Operating hereby jointly and severally represent and warrant to
Banks and Administrative Agent as follows:

         4.1.     REAFFIRM EXISTING REPRESENTATIONS AND WARRANTIES. Each
representation and warranty of each Credit Party contained in the Credit
Agreement and the other Loan Papers is true and correct on the date hereof and
will be true and correct after giving effect to the amendments set forth in
Section 1 hereof.

         4.2.     DUE AUTHORIZATION; NO CONFLICT. The execution, delivery and
performance by Borrower and Operating of this Second Amendment are within
Borrower's and Operating's corporate and partnership powers (as applicable),
have been duly authorized by all necessary action, require no action by or in
respect of, or filing with, any governmental body, agency or official and do not
violate or constitute a default under any provision of applicable law or any
Material Agreement binding upon Borrower, Operating or any other Credit Party or
result in the

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creation or imposition of any Lien upon any of the assets of any Credit Party
except Permitted Encumbrances.

         4.3.     VALIDITY AND ENFORCEABILITY; EXTENSION OF LIENS. This Second
Amendment constitutes the valid and binding obligation of Borrower and Operating
enforceable in accordance with its terms, except as (i) the enforceability
thereof may be limited by bankruptcy, insolvency or similar laws affecting
creditor's rights generally, and (ii) the availability of equitable remedies may
be limited by equitable principles of general application.

         4.4.     NO DEFAULT OR EVENT OF DEFAULT. No Default or Event of Default
has occurred which is continuing.

         SECTION 5. MISCELLANEOUS.

         5.1.     REAFFIRMATION OF LOAN PAPERS. Any and all of the terms and
provisions of the Credit Agreement and the Loan Papers shall, except as amended
and modified hereby, remain in full force and effect. The amendments
contemplated hereby shall not limit or impair any Liens securing the
Obligations, each of which are hereby ratified, affirmed and extended to secure
the Obligations as they may be modified pursuant hereto.

         5.2.     PARTIES IN INTEREST. All of the terms and provisions of this
Second Amendment shall bind and inure to the benefit of the parties hereto and
their respective successors and assigns.

         5.3.     LEGAL EXPENSES. Borrower hereby agrees to pay on demand all
reasonable fees and expenses of counsel to Administrative Agent incurred by
Administrative Agent in connection with the preparation, negotiation and
execution of this Second Amendment and all related documents.

         5.4.     COUNTERPARTS. This Second Amendment may be executed in
counterparts, and all parties need not execute the same counterpart; however, no
party shall be bound by this Second Amendment until Borrower, Operating and
Required Banks have executed a counterpart. Facsimiles shall be effective as
originals.

         5.5.     COMPLETE AGREEMENT. THIS SECOND AMENDMENT, THE CREDIT
AGREEMENT AND THE OTHER LOAN PAPERS REPRESENT THE FINAL AGREEMENT AMONG THE
PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR
ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN
OR AMONG THE PARTIES.

         5.6.     HEADINGS. The headings, captions and arrangements used in this
Second Amendment are, unless specified otherwise, for convenience only and shall
not be deemed to limit, amplify or modify the terms of this Second Amendment,
nor affect the meaning thereof.

         5.7.     EFFECTIVENESS. This Second Amendment shall be effective
automatically and without necessity of any further action by Borrower,
Operating, Administrative Agent or Banks when counterparts hereof have been
executed by Borrower, Operating and Required Banks, and all conditions to the
effectiveness hereof set forth herein have been satisfied.

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         IN WITNESS WHEREOF, the parties hereto have caused this Second
Amendment to be duly executed by their respective Authorized Officers on the
date and year first above written.

                           [Signature pages to follow]

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                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BORROWER:

ENCORE ACQUISITION COMPANY,
a Delaware corporation

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: ASSISTANT TREASURER

OPERATING:

ENCORE OPERATING, L.P.,
a Texas limited partnership

BY:   EAP Operating, Inc.,
      a Delaware corporation,
      its sole general partner

      By:   [ILLEGIBLE]
      Name: [ILLEGIBLE]
      Title: ASSISTANT TREASURER

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

ADMINISTRATIVE AGENT:

FLEET NATIONAL BANK,
as Administrative Agent

By:  [ILLEGIBLE]
     [ILLEGIBLE]
     Director

BANK:

FLEET NATIONAL BANK,
as a Bank

By:  [ILLEGIBLE]
     [ILLEGIBLE]
     Director

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

WACHOVIA BANK, N.A.

By:    /s/  David Humphreys
       ---------------------------
Name:  David Humphreys
Title: Vice President

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

FORTIS CAPITAL CORP.

By:    /s/ David Montgomery
       --------------------
Name:  DAVID MONTGOMERY
Title: SENIOR VICE PRESIDENT

By:    /s/ Darrell W. Holley
       ---------------------
Name:  DARRELL W. HOLLEY
Title: MANAGING DIRECTOR

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

BNP PARIBAS

By:    /s/ David Dodd
       ---------------------
Name     DAVID DODD
Title:    DIRECTOR

By:    /s/ Polly Schott
       --------------------
Name      POLLY SCHOTT
Title:   VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

CREDIT SUISSE FIRST BOSTON,
acting through its CAYMAN ISLANDS BRANCH

By:    /s/ James P. Moran
       ------------------
Name:    JAMES P. MORAN
Title:      DIRECTOR

By:    /s/ David J. Dodd
       ------------------
Name:     DAVID J. DODD
Title:       ASSOCIATE

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

THE FROST NATIONAL BANK

By:     /s/ John s. Warren
        -------------------
Name:     JOHN S. WARREN
Title: SENIOR VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

COMMERCIAL BANK

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

UNION BANK OF CALIFORNIA N.A.

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: AVP

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

CREDIT LYONNAIS NEW YORK BRANCH

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: SENIOR VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

COMPASS BANK

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: SENIOR VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

SUNTRUST BANK

By:    /s/ JAMES M. WARREN
       -------------------
Name:    JAMES M. WARREN
Title:      DIRECTOR

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

RZB FINANCE LLC

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: VICE PRESIDENT

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: ASSISTANT VICE PRESIDENT

                                [Signature Page]

<PAGE>

                                 SIGNATURE PAGE
                                       TO
                      SECOND AMENDMENT TO CREDIT AGREEMENT
                                  BY AND AMONG
                           ENCORE ACQUISITION COMPANY,
                             ENCORE OPERATING, L.P.,
                  FLEET NATIONAL BANK, AS ADMINISTRATIVE AGENT,
                          AND THE BANKS A PARTY THERETO

BANK:

BANK OF SCOTLAND

By:    [ILLEGIBLE]
Name:  [ILLEGIBLE]
Title: FIRST VICE PRESIDENT

                                [Signature Page]