<PAGE>   1
                                                                   EXHIBIT 10(j)




                         Dated as of November 22, 1996


Plains Marketing & Transportation Inc.
1600 Smith Street
Houston, TX 77002

    Re:      Amendment No. 4 to Uncommitted Secured
             Demand Transactional Line of Credit Facility

Gentlemen:

    Reference is made to that certain letter agreement outlining the parameters
of an uncommitted secured demand transactional line of credit facility dated
August 23, 1995 (as further amended to date and including all exhibits,
schedules and annexes thereto, the "Marketing Letter Agreement") among The
First National Bank of Boston ("FNBB"), Internationale Nederlanden (U.S.)
Capital Corporation ("ING"), Den Norske Bank ASA, Comerica Bank-Texas and such
other banks as may from time to time become parties thereto, (collectively, the
"Lenders") and FNBB, as agent for the Lenders (in such capacity, the "Agent")
and Plains Marketing & Transportation Inc. (the "Borrower").  All capitalized
terms used herein without definition which are defined in the Marketing Letter
Agreement shall have the same meaning herein as therein.

    Wells Fargo Bank (Texas), National Association ("Wells") wishes to become a
party to the Marketing Letter Agreement as a Lender to the Borrower and
simultaneously with the execution hereof will execute an Instrument of
Accession in substantially the form attached as Exhibit A to the Marketing
Letter Agreement.

    Borrower, the Lenders (which term for all purposes in this Amendment shall
include Wells) and the Agent wish to amend certain terms of the Marketing
Letter Agreement as follows:

    1.       FACILITY AMOUNT.  Section 1(b) of the Marketing Letter Agreement
is hereby amended by deleting the first sentence thereof and substituting the
following therefor:

         "The aggregate amount of the Accommodations which may be made
         available by the Lenders and which will be allowed to be outstanding
         at any one time under the Marketing Facility shall be restricted to
         the excess of (i) $90,000,000 (subject to adjustment as set forth in
         the proviso below) over (ii) the then aggregate amount of the
         outstanding
<PAGE>   2
                                      -2-

         Accommodations made by the Lenders to or for the account of PMCT Inc.,
         a Delaware corporation ("PMCT"), under that certain letter agreement
         of even date herewith, as amended and in effect from time to time (the
         "PMCT AGREEMENT"), among the Lenders, the Agent and PMCT (such
         difference in amount, as in effect from time to time under the
         Marketing Facility, hereinafter referred to as the "MARKETING FACILITY
         AMOUNT"); provided that for purposes of determining the Marketing
         Facility Amount, the amount set forth in clause (i) of this Section
         1(b) shall be limited to $80,000,000 until such time as the Agent
         shall have received, in form and substance satisfactory to the Agent,
         a copy of an amendment to the Resources Credit Agreement duly executed
         by all parties thereto pursuant to which the lenders under the
         Resources Credit Agreement consent to the increase to $90,000,000 of
         the maximum aggregate Marketing Facility Amount available under the
         Marketing Facility subject to decreases as provided in clause (ii)
         above and the guaranty by Resources of such maximum Marketing Facility
         Amount."

         2.      EXPIRATION DATE.  Section 1(e)(i) of the Marketing Letter
Agreement is hereby amended and restated in its entirety to read as follows:

         "(e)             EXPIRATION: (i) No request for any Accommodation may
                 be made after November 21, 1997, unless the Lenders, in their
                 sole discretion and without any obligation to do so, extend
                 such date in writing."

         3.      RESOURCES CREDIT AGREEMENT.  Section 1(j)(vi) of the Marketing
Letter Agreement is hereby amended by deleting the phrase "that certain Second
Amended and Restated Credit Agreement dated as of February 11, 1994" and
substituting therefor the phrase "that certain Third Amended and Restated
Credit Agreement dated as of April 11, 1996", which Third Amended and Restated
Credit Agreement shall be the agreement referred to in the Marketing Letter
Agreement as the "Resources Credit Agreement".

         4.      CUSHING TERMINAL REPORT.  Section 1(j) of the Marketing Letter
Agreement is hereby amended by renumbering the current clause (ix) to be clause
(x) and by inserting the following paragraph as a new clause (ix):

                 "(ix)    on a monthly basis, a certificate signed by the
                 Borrower's chief financial officer, chief accounting officer
                 or chief operating officer certifying that as of a date which
                 shall be not more than one week prior to the date of the
                 certificate the aggregate sum of (i) the aggregate current
                 crude oil inventory volumes held by the Borrower and/or PMCT,
                 plus (ii) the aggregate volume of current crude oil positions
                 subject to time spreads as described in paragraph (v)(D) of
                 Schedule 4 of the Marketing Letter Agreement for both the
                 Borrower and PMCT, plus (iii) the aggregate volume of all
                 current cash and carry crude oil positions for both the
                 Borrower and PMCT, plus (iv) the aggregate volume of all crude
                 oil which the
<PAGE>   3
                                      -3-

                 Borrower and/or PMCT is otherwise obligated to take pursuant
                 to the terms of existent contracts, does not exceed the then
                 currently available crude oil storage capacity at the Cushing
                 Terminal; and"

         5.      SCHEDULE 1.  Schedule 1 to the Marketing Letter Agreement is
hereby amended by substituting therefor the Schedule 1 attached hereto.

         6.      FINANCIAL AND OTHER GUIDELINES.  Schedule 4 to the Marketing
Letter Agreement is hereby amended as follows:

         (a)     paragraph (v)(C) of Schedule 4 is amended by deleting the text
thereof in its entirety and substituting the following therefor:

         "(C)             The aggregate of (a) crude oil pipeline inventory and
                 (b) crude oil inventory in the Cushing Terminal shall not
                 exceed, in the aggregate for both PMCT Inc. and Marketing, a
                 maximum of 250,000 barrels and such barrels shall be hedged
                 (i) on the NYMEX for delivery within the next 6 months;
                 provided that of such aggregate amount up to 100,000 barrels
                 may be hedged on the NYMEX for delivery between the next 6 and
                 12 months or (ii) in the cash market with counterparties
                 satisfactory to the Lenders for delivery within the next 60
                 days.  Notwithstanding the above, inventories in crude oil
                 pipelines shall be limited to 175,000 barrels."

         (b)     paragraph (v)(D) of Schedule 4 is amended by deleting the text
thereof in its entirety and substituting the following therefor:

         "(D)             Inventory positions (other than fully hedged
                 cash-and-carry positions which qualify under subsection (C)
                 above) and positions which do not otherwise qualify under
                 subsection (C) above shall be limited to time spreads for
                 periods up to a maximum of twelve months for up to a maximum
                 of 500,000 barrels, in the aggregate for both PMCT Inc. and
                 Marketing, of crude oil hedged on the NYMEX."

         (c)              paragraph (xi) of Schedule 4 is amended by deleting
from the first sentence thereof the phrase "that certain Indenture dated as of
October 1, 1992 among Resources, certain subsidiaries and Ameritrust Texas
National Association" and substituting therefor the phrase "that certain
Indenture dated as of March 15, 1996 among Resources, certain subsidiaries of
Resources and Texas Commerce Bank National Association as Trustee, pursuant to
which Resources issued 10 1/4% Senior Subordinated Notes due 2006, Series A and
Series B, in the aggregate principal amount of $150,000,000".
<PAGE>   4
                                      -4-

         7.      SECURITY.  The Borrower hereby confirms that the reference to
"Marketing Letter Agreement" in the term "Marketing Obligations" as used in
that certain Security Agreement dated as of August 23, 1995 between Marketing
and the Agent includes the Marketing Letter Agreement as amended hereby and
that references to the Demand Loans and L/C's issued pursuant to the Marketing
Letter Agreement refers to all Demand Loans and L/C's issued pursuant to the
Marketing Letter Agreement, as amended hereby.

         8.      CONDITIONS PRECEDENT.  This Amendment shall become effective
upon receipt by the Agent of the following:

         (a)     a counterpart of this Amendment duly signed where indicated
below by each Lender, the Agent, the Borrower and Plains Resources Inc.;

         (b)     a counterpart of the Instrument of Accession duly signed where
indicated by the Borrower and each Lender as indicated thereon, evidencing
Wells' accession to the Marketing Letter Agreement and certain other agreements
referenced therein;

         (c)     a promissory note (the "Wells Note") duly signed by the
Borrower evidencing the Borrower's obligations to repay to Wells the Demand
Loans advanced by Wells and any drawings under the L/C's funded by Wells in
form and substance of Exhibit I to the Marketing Letter Agreement;

         (d)     a counterpart of Amendment No. 4 to the PMCT Agreement duly
signed where indicated by PMCT, each Lender and the Agent;

         (e)     a legal opinion of even date herewith from the Borrower's
general counsel in form and substance satisfactory in all respects to the Agent
and its counsel;

         (f)     evidence satisfactory to the Agent that the execution and
delivery of this Amendment and the Wells Note have been duly authorized by all
necessary corporate action and that the Borrower is validly incorporated and in
good standing in all relevant jurisdictions;

         (g)     an acknowledgment from the lenders under the Resources Credit
Agreement that the terms of that certain letter agreement dated August 23, 1995
from the Agent to ING as Agent under the Resources Credit Agreement are in full
force and effect and applicable to the Marketing Letter Agreement as amended
hereby;

         (h)     a counterpart of the Security Agreement and Assignment of
Hedging Account and Agency Agreement in form and substance satisfactory to the
Agent duly executed by the Borrower, the Agent and Bear, Stearns Securities
Corp. in connection with the Borrower's commodity account #J278 0L60 00757 at
Bear, Stearns Securities Corp; and
<PAGE>   5
                                      -5-

         (i)     a counterpart of the Security Agreement and Assignment of
Hedging Account and Agency Agreement in form and substance satisfactory to the
Agent duly executed by the Borrower, the Agent and Citicorp Futures Corporation
in connection with the Borrower's commodity account #10730 at Citicorp Futures
Corporation.
<PAGE>   6
                                      -6-

         If you agree to and accept the foregoing amendment, please so indicate
by signing a counterpart of this letter and returning it to the Agent.  Upon
satisfaction of the conditions set forth in Section 8 hereof, this Amendment
shall take effect as a binding agreement among us, to be construed and
enforceable in accordance with the laws of The Commonwealth of Massachusetts.



                                        PLAINS MARKETING &
                                        TRANSPORTATION INC.


                                        By:          /s/ Phil Kramer          
                                             ---------------------------------
                                             Phil Kramer, Vice President      
                                                                              
                                                                              
                                        THE FIRST NATIONAL BANK OF BOSTON,    
                                        Individually and as Agent             
                                                                              
                                                                              
                                        By:          /s/ Christopher Holmgren 
                                             ---------------------------------
                                                Christopher Holmgren, Director
                                                                              
                                                                              
                                                                              
                                        INTERNATIONALE NEDERLANDEN (U.S.)     
                                        CAPITAL CORPORATION                   
                                                                              
                                                                              
                                        By:          /s/ Robi Artman-Hodge    
                                             ---------------------------------
                                                Robi Artman-Hodge, Managing   
                                                Director                      
                                                                              
                                                                              
                                                                              
DEN NORSKE BANK ASA                     DEN NORSKE BANK ASA                   
                                                                              
                                                                              
By:   /s/  William V. Moyer             By:          /s/ Byron L. Cooley      
   ---------------------------------        ----------------------------------
    William V. Moyer, Vice President        Byron L. Cooley, Senior Vice      
                                            President                         
                                                                              
<PAGE>   7
                                      -7-


                                        COMERICA BANK-TEXAS


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



                                        WELLS FARGO BANK (TEXAS),
                                         NATIONAL ASSOCIATION


                                        By:        /s/ Ann M. Rhoades          
                                             ----------------------------------
                                               Ann M. Rhoades, Vice President

<PAGE>   8
                                      -8-

                            RATIFICATION OF GUARANTY


    The undersigned Guarantor acknowledges and accepts the foregoing Amendment
and ratifies and confirms in all respects such Guarantor's obligations under
the Guaranty dated as of August 23, 1995 (the "Guaranty") executed and
delivered by the Guarantor to the Agent and the Lenders.  The undersigned
Guarantor further agrees that references in the Guaranty to the Resources
Credit Agreement shall be references to the Third Amended and Restated Credit
Agreement dated as of April 11, 1996 among the undersigned Guarantor, ING as
agent and the lenders named therein.


PLAINS RESOURCES INC.


By:         /s/ Phil Kramer               
     --------------------------------
Title:   Vice President
<PAGE>   9
                                      -9-


SCHEDULE 1

LENDER PERCENTAGES


<TABLE>
<CAPTION>
 Lender                                                         Percentage
 ------                                                         ----------
 <S>                                                            <C>       
 The First National Bank of Boston                              30.555556%

 Internationale Nederlanden (U.S.)                                        
   Capital Corporation                                          30.555556%

 Den Norske Bank ASA                                            16.666667%
                                                                          
 Comerica Bank - Texas                                          11.111111%

 Wells Fargo Bank (Texas),                                                
   National Association                                         11.111111%
                                                                ==========
                                                                   100%   
</TABLE>