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                                                                   EXHIBIT 10(t)

                              FIFTH AMENDMENT TO
                 FOURTH AMENDED AND RESTATED CREDIT AGREEMENT


     THIS FIFTH AMENDMENT TO FOURTH AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") dated as of the 1/st/ day of December, 1999, 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 under the Original
                                 -----
Agreement (as defined 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 and a Third Amendment to Fourth Amended and Restated Credit
Agreement dated June 21, 1999 and a Fourth Amendment to Fourth Amended and
Restated Credit Agreement dated September 15, 1999 (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 Fifth Amendment to Fourth Amended and
          Restated Credit Agreement.

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

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


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

     (S) 2.1.  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; (ii) any Investment represented by, or required to comply
     with the obligations undertaken under, the Stock Purchase Agreement
     described in Section 8.35(c) and (iii) loans by the Company to PAAI of up
     to $50,000,000 of the proceeds of any preferred stock of the Company issued
     after December 1, 1999;

                  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 Majority Lenders, 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:

               (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, subject to the amendment of certain of the Schedules
     to the Credit Agreement as attached hereto. 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

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     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 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.

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     (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 DOCUMENTS
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SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
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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.

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

                              PLAINS RESOURCES INC.

                              By: /s/ Michael R. Patterson
                                 ------------------------------------
                                 Name:  Michael R. Patterson
                                 Title: Vice President


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

                              By: /s/ Paul N. Riddle
                                 ------------------------------------
                                 Name:  Paul N. Riddle
                                 Title: Senior Vice President


                              BANKBOSTON, N.A., Lender

                              By: /s/ Terry Ronan
                                 ------------------------------------
                                 Terrence Ronan, Vice President


                              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/ Ann Rhoads
                                 ------------------------------------
                                 Name:  Ann Rhoads
                                 Title: Vice President


                              CHASE BANK OF TEXAS, N.A., Lender

                              By: /s/
                                 ------------------------------------
                                 Name:
                                 Title:

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                              COMERICA BANK-TEXAS, Lender

                              By: /s/ Daniel G. Steele
                                 ------------------------------------
                                 Name:  Daniel G. Steele
                                 Title: Senior Vice President


                              MEESPIERSON CAPITAL CORP., Lender

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

                              By: /s/ Karlo Louman
                                 ------------------------------------
                                 Name:  Karlo Louman
                                 Title: Sr. Managing Director


                              BANK OF SCOTLAND, Lender

                              By: /s/ Jack B. Dykes
                                 ------------------------------------
                                 Name:  Jack B. Dykes
                                 Title: Executive 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/
                                 ------------------------------------
                                 Name:
                                 Title:

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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.
                         CALUMET FLORIDA, INC.
                         PLAINS ILLINOIS INC.


                         By: /s/ Michael R. Patterson
                            -----------------------------------------
                            Name:  Michael R. Patterson
                            Title: Vice President


                         STOCKER RESOURCES, L.P.

                         By:  Stocker Resources, Inc.,
                              its General Partner


                              By: /s/ Michael R. Patterson
                                 ------------------------------------
                                 Name: Michael R. Patterson
                                Title: Vice President

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     The undersigned Subsidiary Guarantor hereby consents to the provisions of
this Agreement 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/ Michael R. Patterson
                                 ------------------------------------
                              Name:  Michael R. Patterson
                              Title: Vice President

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