<PAGE>
 
                                                                   EXHIBIT 10(q)

                              FIFTH AMENDMENT TO
                  THIRD AMENDED AND RESTATED CREDIT AGREEMENT

     THIS FIFTH AMENDMENT TO THIRD AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") dated as of the 3rd day of November, 1997, by and among PLAINS
RESOURCES INC., a Delaware corporation (the "Company"), ING (U.S.) CAPITAL
CORPORATION, f/k/a Internationale Nederlanden (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 Third
Amended and Restated Credit Agreement dated as of April 11, 1996, as amended by
that certain First Amendment to Third Amended and Restated Credit Agreement
dated December 16, 1996, that certain Second Amendment to Third Amended and
Restated Credit Agreement dated March 7, 1997, that certain Third Amendment to
Third Amended and Restated Credit Agreement dated July 18, 1997 and that certain
Fourth Amendment to Third Amended and Restated Credit Agreement dated August 29,
1997 (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 Third Amended and
         Restated Credit Agreement.

               "Amendment Documents" means this Amendment.

                                      -1-
<PAGE>
 
               "Credit Agreement" means the Original Agreement as amended
         hereby.

                           ARTICLE II. -- Amendments

     (S) 2.
1.   Loans.  The proviso in the last sentence of Section 2.01(a) of the Original
Agreement is hereby amended in its entirety to read as follows:

     provided, that no more than six separate Interest Periods in respect of
     Eurodollar Loans may be outstanding at any one time.

     The proviso in the last sentence of Section 2.01(b) of the Original
Agreement is hereby amended in its entirety to read as follows:

     provided, that no more than six separate Interest Periods in respect of
     Eurodollar Loans may be outstanding at any one time.

     (S) 2.2.  Dividend Payments.  Section 8.11 of the Original Agreement is
hereby amended in its entirety to read as follows:

               Section 8.11 Dividend Payments The Company will not, and will not
     permit any of its Subsidiaries to, declare or make any Dividend Payment at
     any time; provided, however, the Company may make regularly scheduled
     Dividend Payments in cash in respect of the Company's Series D Cumulative
     Convertible Preferred Stock, par value $500 per share (a) the aggregate
     amount of all such Dividend Payments not to exceed (i) 6% ($30 per share),
     or (ii) in the event the purchaser thereof shall desire to sell such stock
     in a secondary offering, and the investment bankers representing such
     purchaser shall issue a written opinion to the Company that the gross
     proceeds of such secondary offering shall not exceed $23,300,000, such
     percentage as is necessary to enable such Purchaser to receive $23,300,000
     of gross proceeds from such secondary offering, but in no event exceeding
     7.5% ($37.50 per share)) in any one fiscal year , and (b) the aggregate
     stated value of such outstanding Convertible Preferred Stock at issuance
     not to exceed $23,300,000.

                  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 Agent shall have received, at
Agent's office, a counterpart of this Amendment executed and delivered by the
Company and Majority Lenders.

                 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:

                                      -2-
<PAGE>
 
               (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.

               (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 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 

                                      -3-
<PAGE>
 
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 DOCUMENTS
SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF
NEW YORK AND ANY APPLICABLE LAWS OF THE UNITED STATES OF AMERICA IN ALL
RESPECTS, INCLUDING CONSTRUCTION, VALIDITY AND PERFORMANCE.

     (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/ PHILLIP D. KRAMER
                                        ---------------------------------
                                     Phillip D. Kramer
                                     Vice President and Chief Financial Officer

                                      -4-
<PAGE>
 
                                     ING (U.S.) CAPITAL CORPORATION,
                                     f/k/a Internationale Nederlanden (U.S.)
                                     Capital Corporation, individually as a 
                                     Lender and as Agent


                                     By: /s/ CHRISTOPHER R. WAGNER
                                        ---------------------------------
                                        Christopher R. Wagner, Vice President


                                     BANKBOSTON, N.A., Lender


                                     By: /s/ TERRENCE RONAN
                                        ---------------------------------
                                        Name:   Terrence Ronan
                                        Title:  Vice President


                                     DEN NORSKE BANK ASA, Lender


                                     By: /s/ J. MORTEN KREUTZ
                                        ---------------------------------
                                        Name:   J. Morten Kreutz
                                        Title:  Vice President

                                     By: /s/ WILLIAM V. MOYER
                                        ---------------------------------
                                        Name:   William V. Moyer
                                        Title:  First Vice President


                                     WELLS FARGO BANK (TEXAS),
                                     NATIONAL ASSOCIATION
                                     (f/k/a First Interstate Bank of 
                                     Texas, N.A.), Lender


                                     By: /s/ ANN M. RHOADS
                                        ---------------------------------
                                        Ann M. Rhoads, Vice President

                                      -5-
<PAGE>
 
                                     TEXAS COMMERCE BANK NATIONAL 
                                     ASSOCIATION, Lender


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

                                     COMERICA BANK-TEXAS, Lender


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

                                      -6-
<PAGE>
 
                             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 April 11, 1996 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 MARKETING & TRANSPORTATION INC.
                            PLAINS RESOURCES INTERNATIONAL INC.
                            PLAINS TERMINAL & TRANSFER CORPORATION
                            PLX CRUDE LINES INC.
                            STOCKER RESOURCES, INC.
                            PLX INGLESIDE INC.
                            CALUMET FLORIDA, INC.
                            PLAINS ILLINOIS INC.


                            By: /s/ PHILLIP D. KRAMER
                               ------------------------------------
                               Phillip D. Kramer
                               Vice President and Chief Financial Officer


                            STOCKER RESOURCES, L.P.

                            By:  Stocker Resources, Inc.,
                                 its General Partner


                            By:  /s/ PHILLIP D. KRAMER
                               ------------------------------------
                               Phillip D. Kramer
                               Vice President and Chief Financial Officer

                                      -7-