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                                                                   EXHIBIT 10.1

                              SIXTH AMENDMENT TO
                 FOURTH AMENDED AND RESTATED CREDIT AGREEMENT

     THIS SIXTH AMENDMENT TO FOURTH AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") dated as of the 12th day of June, 2000, by and among PLAINS
 ---------
RESOURCES INC., a Delaware corporation (the "Company"), FIRST UNION NATIONAL
                                             -------
BANK (assignee of ING (U.S.) Capital LLC, successor in interest to ING (U.S.)
Capital Corporation), as Agent ("Agent"), and the Lenders named herein.
                                 -----

                             W I T N E S S E T H:

     WHEREAS, the Company, Agent and Lenders entered into that certain Fourth
Amended and Restated Credit Agreement dated as of May 22, 1998, as amended by a
First Amendment to Fourth Amended and Restated Credit Agreement dated November
17, 1998, a Second Amendment to Fourth Amended and Restated Credit Agreement
dated March 15, 1999, a Third Amendment to Fourth Amended and Restated Credit
Agreement dated June 21, 1999, a Fourth Amendment to Fourth Amended and Restated
Credit Agreement dated September 15, 1999, a Fifth Amendment to Fourth Amended
and Restated Credit Agreement dated December 1, 1999 and a Limited Waiver and
Consent dated as of January 28, 2000 (as amended, the "Original Agreement") for
                                                       ------------------
the purposes and consideration therein expressed, pursuant to which Lenders
became obligated to make and made loans to the Company as therein provided; and

     WHEREAS, the Company, Agent and Lenders desire to amend the Original
Agreement for the purposes described herein;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein and in the Original Agreement, in consideration
of the loans which may hereafter be made by Lenders to the Company, and for
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto do hereby agree as follows:

                   ARTICLE I. -- Definitions and References
                                  --------------------------

     (S) 1.1.  Terms Defined in the Original Agreement.  Unless the context
               ---------------------------------------
otherwise requires or unless otherwise expressly defined herein, the terms
defined in the Original Agreement shall have the same meanings whenever used in
this Amendment.

     (S) 1.2.  Other Defined Terms.  Unless the context otherwise requires, the
               -------------------
following terms when used in this Amendment shall have the meanings assigned to
them in this (S) 1.2.

               "Amendment" means this Sixth Amendment to Fourth Amended and
                ---------
      Restated Credit Agreement.

               "Amendment Documents" means this Amendment.
                -------------------

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          "Credit Agreement" means the Original Agreement as amended hereby.
           ----------------

                           ARTICLE II. -- Amendments
                                          ----------

     (S) 2.1.   Definitions.  The definitions of "Revolving Credit Termination
                -----------
Date" and "Tangible Net Worth" set forth in Section 1.01 of the Original
Agreement are hereby amended in their entirety to read as follows:

               "Revolving Credit Termination Date" shall mean the earlier of (a)
                ---------------------------------
     July 1, 2002 and (b) the date on which the Commitment is reduced to zero or
     terminated pursuant to Section 2.03 hereof.

               "Tangible Net Worth" shall mean, as at any date, the sum for the
                ------------------
     Company and its Consolidated Subsidiaries (determined on a consolidated
     basis without duplication in accordance with GAAP), of the following:

                    (a) the amount of capital stock, plus
                                                     ----

                    (b) the amount of surplus and retained earnings (or in the
          case of a surplus or retained earnings deficit, minus the amount of
                                                          -----
          such deficit), minus
                         -----

                    (c) the sum of the following: cost of treasury shares and
          the book value of all assets which should be classified as intangibles
          (without duplication of deductions in respect of items already
          deducted in arriving at surplus and retained earnings) but in any
          event including goodwill, research and development costs, trademarks,
          trade names, copyrights, patents and franchises, unamortized debt
          discount and expense, all reserves and any write-up in the book value
          of assets resulting from a revaluation thereof subsequent to December
          31, 1997.

     The effect of any increase or decrease in net worth in any period as a
     result of items of income or loss not reflected in the determination of net
     income but reflected in the determination of comprehensive income (to the
     extent provided under GAAP (x) as in effect on June 12, 2000 or (y) to
     become effective after such date under rules currently proposed as of such
     date that become effective on or before January 1, 2001) shall be excluded
     in determining Tangible Net Worth.

     The following definition of "PAAI Transfer" is hereby added to Section 1.01
of the Original Agreement immediately following the definition of "PAAI":

          "PAAI Transfer" shall mean the occurrence of any of the following:
           -------------

     (i)  The Company, either directly or indirectly, shall cease to be the
          legal and beneficial owner of 100% of the outstanding capital stock of
          PAAI or 100% of the outstanding limited liability company interests of
          PAAI, LLC.

     (ii) PAAI shall cease to be the legal and beneficial owner of 75% or more
          of the general partner interests (including all securities which are
          convertible into

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               general partner interests) of the MLP, Plains Marketing LP or All
               American Pipeline LP.

      (iii)    The Company or any of its Subsidiaries, PAAI or PAAI, LLC, or any
               successor (by conversion, merger or otherwise) of any of them, or
               any combination of the foregoing Persons, either directly or
               indirectly, shall cease to be the legal and beneficial owner of
               75% or more in the aggregate of the number of limited partner
               units of the MLP owned, either directly or indirectly, by the
               Company or any of its Subsidiaries, PAAI, PAAI, LLC or each
               successor (by conversion, merger or otherwise) of each of them,
               or any combination of the foregoing Persons, in the aggregate as
               of June 12, 2000.

     (S) 2.2.  Borrowing Base Redeterminations.  The first sentence of
               -------------------------------
Section 2.08(b) of the Original Agreement is hereby amended in its entirety to
read as follows:

               (b)  Supermajority Lenders shall endeavor on each May 1 and
     October 1, commencing on October 1, 1998, and may at any time upon the
     occurrence of any event or change which in the reasonable judgment of such
     Supermajority Lenders would have a Material Adverse Effect or a material
     adverse change in the value or nature of the Oil and Gas Properties
     included in the Borrowing Base from the most recent redetermination
     pursuant to this Section 2.08 or upon the incurrence of additional
     Subordinated Indebtedness, of not less than $10,000,000, or upon a PAAI
     Transfer, redetermine the amount of the Borrowing Base in accordance with
     this Section 2.08.

     (S) 2.3.  Repayment of Term Loans.  Section 3.01(b) of the Original
               -----------------------
Agreement is hereby amended in its entirety to read as follows:

               (b)  The Company will repay the principal of the Term Loans in
     twelve installments payable on each Quarterly Date beginning October 1,
     2002, with the final installment being due and payable on or before July 1,
     2005. Each such installment shall be equal to one-twelfth of the original
     principal amount of the Term Loans as of the Revolving Credit Termination
     Date. In any event all unpaid principal and interest shall be due and
     payable in full on the final maturity of July 1, 2005. As set forth in
     Section 2.07(c), all optional and mandatory prepayments made on the Term
     Loans shall be applied to the scheduled installments in inverse order of
     their maturity.

     (S) 2.4.  Investments.  Section 8.10(f) of the Original Agreement is
               -----------
hereby amended in its entirety to read as follows:

               (f)  in addition to any capital contributions permitted in
     subsection (e) above, the following Investments in Unrestricted
     Subsidiaries: (i) capital contributions of up to $85,000,000 of the
     proceeds of any preferred or common stock of the Company issued after
     January 1, 1998; and (ii) any Investment represented by, or required to
     comply with the obligations undertaken under, the Stock Purchase Agreement
     described in Section 8.35(c).

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     (S) 2.5.  Dividend Payments.  Section 8.11 of the Original Agreement is
               -----------------
hereby amended by (i) deleting the term "and" at the end of clause (a) thereof,
(ii) deleting the period at the end of clause (b) thereof and substituting
therefor ", and", and (iii) adding clause (c) at the end thereof, to read as
follows:

               (c)  one or more Dividend Payments in cash of up to $50,000,000,
     in the aggregate, to purchase, redeem, retire or otherwise acquire any
     shares of any one or more classes of stock of the Company, provided, (i) if
                                                                --------
     the affected class of stock requires that a notice be given or similar
     condition otherwise be met prior to its purchase, redemption, retirement or
     other acquisition, no Default existed on the date that any such notice was
     given or similar condition otherwise was met, or (ii) if the affected class
     of stock does not require that a notice be given or similar condition
     otherwise be met prior to its purchase, redemption, retirement or other
     acquisition, no Default has occurred and is then continuing.

     (S) 2.6.  Tangible Net Worth.  The reference to "$85,000,000" set forth
               ------------------
in clause (a) of Section 8.12 of the Original Agreement is hereby amended to
refer instead to "$85,000,000 minus all Dividend Payments made pursuant to
Section 8.11(c)".

     (S) 2.7.  New Borrowing Base.  Pursuant to Section 2.08 of the Credit
               ------------------
Agreement, Agent hereby notifies the Company that Supermajority Lenders have
redetermined the Borrowing Base as $225,000,000, effective for the period
beginning on and including the date hereof and continuing until but not
including the next date as of which the Borrowing Base is redetermined.

                  ARTICLE III. -- Conditions of Effectiveness
                                  ---------------------------

     (S) 3.1.  Effective Date.  This Amendment shall become effective as of
               --------------
the date first above written when and only when (i) Agent shall have received,
at Agent's office, a counterpart of this Amendment executed and delivered by the
Company and each Lender, and (ii) Agent shall have additionally received all of
the following documents, each document (unless otherwise indicated) being dated
the date of receipt thereof by Agent, duly authorized, executed and delivered,
and in form and substance satisfactory to Agent:

               (A)  Officer's Certificate. A certificate of a duly authorized
                    ---------------------
     officer of the Company to the effect that all of the representations and
     warranties set forth in Article IV hereof are true and correct at and as of
     the date thereof.

               (B)  Supporting Documents. Such supporting documents as Agent may
                    --------------------
     reasonably request.

                 ARTICLE IV. -- Representations and Warranties
                                ------------------------------

     (S) 4.1.  Representations and Warranties of the Company.  In order to
               ---------------------------------------------
induce Agent and Lenders to enter into this Amendment, the Company represents
and warrants to Agent and Lenders that:

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          (a)  The representations and warranties contained in Section 7 of the
     Original Agreement, are true and correct at and as of the time of the
     effectiveness hereof, except to the extent that such representation or
     warranty was made as of a specific date or updated, modified or
     supplemented as of a subsequent date with the consent of Majority Lenders,
     subject to (i) the amendment of certain of the Schedules to the Credit
     Agreement as attached hereto and (ii) in regard to the penultimate sentence
     of Section 7.02, the Unauthorized Trading Losses, as referred to in the
     Company's annual report on Form 10-K for the year ended December 31, 1999.
     No Default has occurred and is continuing.

          (b)  The Company and the Subsidiaries are duly authorized to execute
     and deliver this Amendment and the other Amendment Documents to the extent
     a party thereto, and the Company is and will continue to be duly authorized
     to borrow and perform its obligations under the Credit Agreement. The
     Company and the Subsidiaries have duly taken all corporate action necessary
     to authorize the execution and delivery of this Amendment and the other
     Amendment Documents, to the extent a party thereto, and to authorize the
     performance of their respective obligations thereunder.

          (c)  The execution and delivery by the Company and the Subsidiaries of
     this Amendment and the other Amendment Documents, to the extent a party
     thereto, the performance by the Company and the Subsidiaries of their
     respective obligations hereunder and thereunder, and the consummation of
     the transactions contemplated hereby and thereby, do not and will not
     conflict with any provision of law, statute, rule or regulation or of the
     certificate or articles of incorporation and bylaws of the Company or any
     Subsidiary, or of any material agreement, judgment, license, order or
     permit applicable to or binding upon the Company or any Subsidiary, or
     result in the creation of any lien, charge or encumbrance upon any assets
     or properties of the Company or any Subsidiary, except in favor of Agent
     for the benefit of Lenders.  Except for those which have been duly
     obtained, no consent, approval, authorization or order of any court or
     governmental authority or third party is required in connection with the
     execution and delivery by the Company or any Subsidiary of this Amendment
     or any other Amendment Document, to the extent a party thereto, or to
     consummate the transactions contemplated hereby and thereby.

          (d)  When this Amendment and the other Amendment Documents have been
     duly executed and delivered, each of the Basic Documents, as amended by
     this Amendment and the other Amendment Documents, will be a legal and
     binding instrument and agreement of the Company and the Subsidiaries, to
     the extent a party thereto, enforceable in accordance with its terms,
     (subject, as to enforcement of remedies, to applicable bankruptcy,
     insolvency and similar laws applicable to creditors' rights generally and
     to general principles of equity).

                          ARTICLE V. -- Miscellaneous
                                        -------------

     (S) 5.1.  Ratification of Agreements.  The Original Agreement, as hereby
               --------------------------
amended, is hereby ratified and confirmed in all respects.  The Basic Documents,
as they may be amended or affected by this Amendment and/or the other Amendment
Documents, are hereby ratified and confirmed in all respects.  Any reference to
the Credit Agreement in any Basic Document shall be deemed to refer to this
Amendment also.  The execution, delivery and effectiveness of this

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Amendment and the other Amendment Documents shall not, except as expressly
provided herein or therein, operate as a waiver of any right, power or remedy of
Agent or any Lender under the Credit Agreement or any other Basic Document nor
constitute a waiver of any provision of the Credit Agreement or any other Basic
Document.

     (S) 5.2.  Ratification of Security Documents.  The Company, Agent and
               ----------------------------------
Lenders each acknowledge and agree that any and all indebtedness, liabilities or
obligations arising under or in connection with the Notes are Obligations and is
secured indebtedness under, and is secured by, each and every Security Document
to which the Company is a party.  The Company hereby re-pledges, re-grants and
re-assigns a security interest in and lien on every asset of the Company
described as collateral in any Security Document.

     (S) 5.3.  Survival of Agreements.  All representations, warranties,
               ----------------------
covenants and agreements of the Company herein and in the other Amendment
Documents shall survive the execution and delivery of this Amendment and the
other Amendment Documents and the performance hereof and thereof, including
without limitation the making or granting of each Loan, and shall further
survive until all of the Obligations are paid in full.  All statements and
agreements contained in any certificate or instrument delivered by the Company
or any Subsidiary hereunder, under the other Amendment Documents or under the
Credit Agreement to Agent or any Lender shall be deemed to constitute
representations and warranties by, or agreements and covenants of, the Company
under this Amendment and under the Credit Agreement.

     (S) 5.4.  Basic Documents.  This Amendment and each of the other
               ---------------
Amendment Documents is a Basic Document, and all provisions in the Credit
Agreement pertaining to Basic Documents apply hereto and thereto.

     (S) 5.5.  GOVERNING LAW.  THIS AMENDMENT AND THE OTHER AMENDMENT
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DOCUMENTS SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
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STATE OF NEW YORK AND ANY APPLICABLE LAWS OF THE UNITED STATES OF AMERICA IN ALL
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RESPECTS, INCLUDING CONSTRUCTION, VALIDITY AND PERFORMANCE.
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     (S) 5.6.  Counterparts.  This Amendment and each of the other Amendment
               ------------
Documents may be separately executed in counterparts and by the different
parties hereto in separate counterparts, each of which when so executed shall be
deemed to constitute one and the same Amendment or Amendment Document, as the
case may be.

     IN WITNESS WHEREOF, this Amendment is executed as of the date first above
written.

                              PLAINS RESOURCES INC.

                              By: /s/ Phil Kramer
                                 --------------------------------------------
                                 Phil Kramer, Executive Vice President

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                              FIRST UNION NATIONAL BANK,
                              as Agent, LC Issuer and a Lender

                              By: /s/ Robert R. Wetteroff
                                 -------------------------------------------
                                 Robert R. Wetteroff, Senior Vice President


                              FLEET NATIONAL BANK
                              (f/k/a BankBoston, N.A.), Lender

                              By: /s/ Terrence Ronan
                                 -------------------------------------------
                                 Terrence Ronan, Director


                              BANK OF AMERICA, N.A., Lender

                              By: /s/ Irene C. Rummel
                                 -------------------------------------------
                                 Name:  Irene C. Rummel
                                 Title: Vice President


                              WELLS FARGO BANK (TEXAS),
                              NATIONAL ASSOCIATION, Lender

                              By: /s/ John B. Lane
                                 -------------------------------------------
                                 Name:  John B. Lane
                                 Title: Vice President


                              CHASE BANK OF TEXAS, N.A., Lender

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


                              COMERICA BANK-TEXAS, Lender

                              By: /s/ Martin W. Wilson
                                 -------------------------------------------
                                 Martin W. Wilson, Vice President

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                              MEESPIERSON CAPITAL CORP., Lender

                              By: /s/ Darrell W. Holley
                                 -------------------------------------------
                                 Name:  Darrell W. Holley
                                 Title: Managing Director

                              By: /s/ Richard Herrick
                                 -------------------------------------------
                                 Name:  Richard Herrick
                                 Title: Senior Vice President


                              BANK OF SCOTLAND, Lender

                              By: /s/ Annie Glynn
                                 -------------------------------------------
                                 Name:  Annie Glynn
                                 Title: Senior Vice President


                              U.S. BANK NATIONAL ASSOCIATION, Lender

                              By: /s/ Monte E.. Deckerd
                                 -------------------------------------------
                                 Name:  Monte E. Deckerd
                                 Title: Vice President


                              HIBERNIA NATIONAL BANK

                              By: /s/ David R. Reid
                                 -------------------------------------------
                                 Name:  David R. Reid
                                 Title: Senior Vice President


                              GENERAL ELECTRIC CAPITAL CORPORATION

                              By: /s/ Paul A. Jordan
                                 -------------------------------------------
                                 Name:  Paul A. Jordan
                                 Title: Portfolio Manager

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                             CONSENT AND AGREEMENT
                             ---------------------

     Each of the undersigned Subsidiary Guarantors hereby consents to the
provisions of this Amendment and the transactions contemplated herein and hereby
(i) acknowledges and agrees that any and all indebtedness, liabilities or
obligations arising under or in connection with the Notes are Obligations and
are secured indebtedness under, and are secured by, each and every Security
Document to which it is a party, (ii) re-pledges, re-grants and re-assigns a
security interest in and lien on all of its assets described as collateral in
any Security Document, (iii) ratifies and confirms its Amended and Restated
Guaranty dated May 22, 1998 made by it for the benefit of Agent and Lenders, and
(iv) expressly acknowledges and agrees that such Subsidiary Guarantor guarantees
all indebtedness, liabilities and obligations arising under or in connection
with the Notes pursuant to the terms of such Amended and Restated Guaranty, and
agrees that its obligations and covenants thereunder are unimpaired hereby and
shall remain in full force and effect.

                      PLAINS RESOURCES INTERNATIONAL INC.
                      STOCKER RESOURCES, INC.
                      PLAINS ILLINOIS INC.


                      By: /s/ Phil Kramer
                          ----------------------------------------------
                          Phil Kramer, Executive Vice President


                      STOCKER RESOURCES, L.P.

                      By:  Stocker Resources, Inc.,
                           its General Partner


                           By: /s/ Phil Kramer
                               -----------------------------------------
                               Phil Kramer, Executive Vice President

                                       9
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     The undersigned Subsidiary Guarantor hereby consents to the provisions of
this Amendment and the transactions contemplated herein and hereby (i)
acknowledges and agrees that any and all indebtedness, liabilities or
obligations arising under or in connection with the Notes are Obligations and
are secured indebtedness under, and are secured by, each and every Security
Document to which it is a party, (ii) re-pledges, re-grants and re-assigns a
security interest in and lien on all of its assets described as collateral in
any Security Document, (iii) ratifies and confirms its Guaranty dated July 1,
1999 made by it for the benefit of Agent and Lenders, and (iv) expressly
acknowledges and agrees that such Subsidiary Guarantor guarantees all
indebtedness, liabilities and obligations arising under or in connection with
the Notes pursuant to the terms of such Guaranty, and agrees that its
obligations and covenants thereunder are unimpaired hereby and shall remain in
full force and effect.

                                 ARGUELLO INC.


                                 By: /s/ Tim Moore
                                    ------------------------------
                                     Name:  Tim Moore
                                     Title: Vice President

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