<PAGE>   1
                                                                   EXHIBIT 10(k)


                         Dated as of November 22, 1996


PMCT 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 "PMCT 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 PMCT Inc. (the "Borrower").  All capitalized terms used herein without
definition which are defined in the PMCT Letter Agreement shall have the same
meaning herein as therein.

       Wells Fargo Bank (Texas), National Association ("Wells") wishes to
become a party to the PMCT 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 PMCT 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 PMCT
Letter Agreement as follows:

       1.     FACILITY AMOUNT.  Section 1(b) of the PMCT 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 PMCT 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 Accommodations
       made by the Lenders to or for the account of Plains Marketing &
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       Accommodations made by the Lenders to or for the account of Plains
       Marketing and Transportation Inc., a Delaware corporation ("MARKETING"),
       under that certain letter agreement of even date herewith, as amended
       and in effect from time to time (the "MARKETING AGREEMENT"), among the
       Lenders, the Agent and Marketing (such difference in amount, as in
       effect from time to time under the PMCT Facility, hereinafter referred
       to as the "PMCT FACILITY AMOUNT"); provided that for purposes of
       determining the PMCT 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 PMCT Facility Amount available under this PMCT
       Facility subject to decreases as provided in clause (ii) above and the
       guaranty by Resources of such maximum amount of Accommodations available
       under the Marketing Agreement."

       2.     EXPIRATION DATE.  Section 1(e)(i) of the PMCT 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(d)(iii) of the PMCT 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 PMCT Letter Agreement as the
"Resources Credit Agreement".

       4.     CUSHING TERMINAL REPORT.  Section 1(j) of the PMCT Letter
Agreement is hereby amended as follows:

       (a)    by deleting the reference to "Marketing Letter Agreement" in
clause (i) thereof and substituting the phrase "PMCT Letter Agreement"
therefor; and

       (b)    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





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              aggregate sum of (i) the aggregate current crude oil inventory
              volumes held by the Borrower and/or Marketing, 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
              PMCT Letter Agreement for both the Borrower and Marketing, plus
              (iii) the aggregate volume of all current cash and carry crude
              oil positions for both the Borrower and Marketing, plus (iv) the
              aggregate volume of all crude oil which the Borrower and/or
              Marketing 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 PMCT Letter Agreement is hereby
amended by substituting therefor the Schedule 1 attached hereto.

       6.     FINANCIAL AND OTHER GUIDELINES.  Schedule 4 to the PMCT 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




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                                      -4-

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".

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

       (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 PMCT 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 PMCT Letter Agreement;

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

       (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





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under the Resources Credit Agreement are in full force and effect and
applicable to the PMCT 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 Marketing, the Agent and Bear, Stearns Securities Corp. in
connection with Marketing's commodity account #J278 0L60 00751 at Bear, Stearns
Securities Corp; and

       (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 Marketing, the Agent and Citicorp Futures Corporation in
connection with Marketing's commodity account #10730 at Citicorp Futures
Corporation.





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                                      -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.




                                       PMCT 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





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                                      -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





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                                      -8-


SCHEDULE 1

LENDER PERCENTAGES



<TABLE>
 <S>                                                     <C>
 Lender                                                  Percentage
 ------                                                  ----------
 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>