<PAGE>
 
                                                                 

              SEVENTH AMENDMENT TO THIRD RESTATED LOAN AGREEMENT
                                    (TERM)


     THIS SEVENTH AMENDMENT TO THIRD RESTATED LOAN AGREEMENT (TERM) (herein
called the "Amendment") made as of the 22nd day of March, 1996, by and among
Western Gas Resources, Inc., a Delaware corporation ("Borrower"), NationsBank of
Texas, N.A., a national banking association, as Agent ("Agent"), and NationsBank
of Texas, N.A., Bankers Trust Company, Bank of Montreal and CIBC Inc. (herein,
collectively referred to as "Lenders"),

                             W I T N E S S E T H:

     WHEREAS, Borrower, Agent and Lenders have entered into that certain Third
Restated Loan Agreement (Term) dated as of August 31, 1993, as amended by that
certain First Amendment to Third Restated Loan Agreement (Term) dated as of
December 31, 1993, that certain Second Amendment to Third Restated Loan
Agreement (Term) dated as of September 2, 1994, that certain Third Amendment to
Third Restated Loan Agreement (Term) dated as of December 2, 1994, that certain
Fourth Amendment to Third Restated Loan Agreement (Term) dated as of February
23, 1995, that certain Fifth Amendment to Third Restated Loan Agreement (Term)
dated as of July 19, 1995, among Borrower, Agent and Lenders, and that certain
Sixth Amendment to Third Restated Loan Agreement (Term) dated as of November 29,
1995, among Borrower, Agent and Lenders (as amended to the date hereof, the
"Original Agreement") for the purpose and consideration therein expressed,
whereby Lenders became obligated to make and made loans to Borrower as therein
provided; and

     WHEREAS, Borrower, Agent and Lenders desire to amend the Original Agreement
as expressly set forth herein;

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

                                      -1-

                                                                   Exhibit 10.54
<PAGE>
 
                   ARTICLE I. -- Definitions and References
                                 --------------------------

     Section 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.

     Section 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 Section 1.2.

          "Amendment" means this Seventh Amendment to Third Restated Loan
           ---------                                                     
     Agreement (Term).

          "Loan Agreement" shall mean the Original Agreement as amended hereby.
           --------------                                                      

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

     Section 2.1.  Definitions.  (a)  The definition of "Preferred Stock" in
                   -----------                                             
Section 1.1 of the Original Agreement is hereby amended in its entirety to read
as follows:

          "`Preferred Stock' means all issued and outstanding preferred stock of
            ---------------                                                     
     Borrower, as the same may change from time to time, including but not
     limited to  (i) the 1,400,000 shares of $2.28 Cumulative Preferred Stock of
     Borrower and (ii) the 2,760,000 shares of $2.625 Cumulative Convertible
     Preferred Stock of Borrower."

     (b)  The definition of "Additional Preferred Stock" is hereby deleted from
Section 1.1 of the Original Agreement.

     Section 2.2.  Limitation on Dividends and Distributions.  Section 5.2(a) of
                   -----------------------------------------                    
the Original Agreement is hereby amended in its entirety to read as follows and
such amendment shall be effective as of December 31, 1995.

          "(a)  Limitation on Dividends and Distributions.  Except for payments
                -----------------------------------------                      
     by Borrower to its stockholders which are permitted under the following
     sentences of this subsection and do not otherwise violate any provisions of
     this Agreement and except for dividends paid to Borrower by its
     Subsidiaries or to MIGC by MGTC, none of Borrower and its Subsidiaries will
     declare or pay any dividends on, or make any other distribution in respect
     of, any class of its capital stock or any partnership or other interest in
     it, other than the distribution of common stock pursuant to the conversion
     or exchange of Preferred Stock, nor will any of Borrower and its
     Subsidiaries directly

                                      -2-
<PAGE>
 
     or indirectly make any capital contribution to or purchase, redeem, acquire
     or retire any shares of the capital stock of or partnership interest in any
     of Borrower and its Subsidiaries (whether such interests are now or
     hereafter issued, outstanding or created) or cause or permit any reduction
     or retirement of the capital stock of or partnership interest in any of
     Borrower and its Subsidiaries.  Borrower may make any of the payments,
     distributions, capital contributions or purchases described above in this
     Section 5.2(a), so long as (i) no Default or Event of Default has occurred
     and is continuing at the time such dividends are declared and paid and (ii)
     such repurchases and dividends declared or paid by Borrower since December
     31, 1995, together with all investments Borrower has made in accordance
     with the provisions of Section 5.2(f)(vi), do not, in the aggregate, exceed
     the sum of (A) $10,000,000; plus (B) fifty percent (50.0%) of Borrower's
                                 ----                                        
     Consolidated cumulative net income earned after December 31, 1995 if such
     figure is positive (zero percent, if there is a Consolidated cumulative net
     loss); plus (C) fifty percent (50.0%) of the cumulative net proceeds
            ----                                                         
     received by Borrower and its Subsidiaries at any time after December 31,
     1995 from the sale of any equity securities issued by Borrower or any of
     its Subsidiaries.  All dividends declared in the fourth Fiscal Quarter of
     1995, payable in 1996 with respect to any class of stock of Borrower, shall
     be permitted and excluded from the preceding calculation."

     Section 2.3.  Limitation on Mergers, Issuances of Securities.  The
                   ----------------------------------------------      
reference to the term "Additional Preferred Stock" in section 5.2(d) of the
Original Agreement is hereby deleted.

     Section 2.4.  Limitation on Investments and New Businesses.  Section 5.2(f)
                   --------------------------------------------                 
of the Original Agreement is hereby amended in its entirety to read as follows
and such amendment shall be effective as of December 31, 1995.

          "(f)  Limitation on Investments and New Businesses.  No Related Person
                --------------------------------------------                    
     will:

                (i) make any expenditure or commitment or incur any obligation
          or enter into or engage in any transaction except in the ordinary
          course of business (which shall be deemed to include expenditures,
          commitments, obligations and transactions permitted by clause (iii),
          (iv), (v) or (vi) of this sentence);

               (ii) engage directly or indirectly in any business or conduct any
          operations except in connection with or incidental to its present
          businesses and operations (which shall be deemed to include
          expenditures, commitments, obligations and transactions permitted by
          clause (iii), (iv), (v) or (vi) of this sentence);

              (iii) make any acquisitions of or capital contributions to or
          other investments in any Persons other than (A) capital contributions
          to and investments in Williston Gas Company and Subsidiaries already
          wholly owned

                                      -3-
<PAGE>
 
          by such Related Person and the joint ventures described on Schedule 4
          hereto, and (B) deposits with any Lender, investments in obligations
          of any Lender or any of such Lender's Affiliates, time deposits in
          other banking institutions which, at the time such deposit is made,
          are rated "C" by Thomson BankWatch, Inc. and investments maturing
          within one year from the date of acquisition in direct obligations of
          or obligations supported by, the full faith and credit of, the United
          States of America,

               (iv) make any significant acquisitions or investments in any
          properties other than gas processing, transmission, gathering and
          storage facilities and domestic oil and gas properties;

                (v) make capital expenditures and/or general and administrative
          expenditures relating to power generation and power marketing which
          exceed in the aggregate $1,000,000, or;

               (vi) make any other investments unless (1) no Default or Event of
                                               ------                           
          Default has occurred and is continuing at the time such investment is
          made and (2) such investments, together with all repurchases and
          dividends declared or paid by Borrower since December 31, 1995 in
          accordance with the provisions of Section 5.2(a) (except for all
          dividends declared in the fourth Fiscal Quarter of 1995, payable in
          1996 with respect to any class of stock of Borrower), do not, in the
          aggregate, exceed the sum of (I) $10,000,000; plus (II) fifty percent
                                                        ----                   
          (50.0%) of Borrower's Consolidated cumulative net income earned after
          December 31, 1995 if such figure is positive (zero percent, if there
          is a Consolidated cumulative net loss); plus (III) fifty percent
                                                  ----                    
          (50.0%) of the cumulative net proceeds received by Borrower and its
          Subsidiaries at any time after December 31, 1995 from the sale of any
          equity securities issued by Borrower or any of its Subsidiaries.

     Notwithstanding the foregoing, if any Related Person makes an acquisition
     of any Person or property in accordance with the provisions of this Section
     5.2(f), and if the historical cash earnings of the Person or property so
     acquired would have to be included in the calculation of the Mandatory
     Prepayment Ratio most recently delivered to Agent and Lenders hereunder to
     support the Indebtedness, if any, incurred by such Related Person in making
     the acquisition, Borrower shall promptly notify Agent and Lenders of such
     fact and Lenders shall have the right to require a recalculation of the
     Mandatory Prepayment Ratio in accordance with the provisions of Section
     2.5(a) which ratio shall become effective at the time of such acquisition."

     Section 2.5.  Events of Default and Remedies.  (a)  All references to the
                   ------------------------------                             
term "Additional Preferred Stock" in section 7.1(i) of the Original Agreement
are hereby deleted.

     (b)  Section 7.1(k) of the Original Agreement is hereby amended in its
entirety to read as follows:

                                      -4-
<PAGE>
 
          "(k) Any event occurs which would require Borrower to redeem for cash
     the Preferred Stock or any subordinated notes which may have been issued in
     exchange for the Preferred Stock, or which gives the holders of the
     Preferred Stock or any subordinated notes which may have been issued in
     exchange for the Preferred Stock the right to demand such redemption; or"

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

     Section 3.1.  Effective Date.  This Amendment shall become effective as of
                   --------------                                              
the date first above written, except as otherwise provided herein, when, and
only when, Agent shall have received, at Agent's office, all of the following:

          (a)  Amendment.  A counterpart of this Amendment executed and
               ---------                                               
     delivered by Borrower and Majority Lenders.

          (b)  Amendment Fee.  An amendment fee equal to one-tenth of one-
               -------------                                             
     percent (0.10%) of the outstanding principal balance of the Loans (as of 
     the date hereof) of each Lender, payable to Agent for the account of each 
     Lender.

          (c) Officer's Certificate.  A certificate of a duly authorized officer
              ---------------------                                             
     of Borrower, dated the date of receipt thereof by Agent, duly authorized,
     executed and delivered, and in form and substance satisfactory to Agent, 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 time of such
     effectiveness.

          (d) Secretary's Certificate.  A certificate of the Secretary or
              -----------------------                                    
     Assistant Secretary of Borrower, dated as of the date of this Amendment,
     duly authorized, executed and delivered, and in form and substance
     satisfactory to Agent, which shall contain the names and signatures of the
     officers of Borrower authorized to execute Loan Documents on behalf of
     Borrower and which shall certify to the truth, correctness and completeness
     of the following exhibits attached thereto:  (i) a copy of resolutions
     adopted by the Board of Directors of Borrower, in full force and effect on
     the date hereof, authorizing the execution, delivery and performance of the
     Loan Documents, including this Amendment, (ii) a copy of Borrower's
     charter, certified by the appropriate official of the State of Delaware,
     and (iii) a copy of the bylaws of Borrower, in full force and effect on the
     date hereof.

          (d)  Legal Opinion.  a favorable opinion from Messr. John Walter,
               -------------                                               
     Esq., counsel for Borrower in a form acceptable to Agent.

                                      -5-
<PAGE>
 
          (e)  Supporting Documents.  such supporting documents as Agent may
               --------------------                                         
     reasonably request.


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

     Section 4.1.  Representations and Warranties of Borrower.  In order to
                   ------------------------------------------              
induce each Lender to enter into this Amendment, Borrower represents and
warrants to each Lender that:

          (a) The representations and warranties contained in each subsection of
     Section 4.1 of the Original Agreement are true and correct at and as of the
     time of the effectiveness hereof.

          (b) Borrower is duly authorized to execute and deliver this Amendment
     and is and will continue to be duly authorized to borrow monies and to
     perform its obligations under the Loan Agreement.  Borrower has duly taken
     all corporate action necessary to authorize the execution and delivery of
     this Amendment and to authorize the performance of the obligations of
     Borrower hereunder.

          (c) The execution and delivery by Borrower of this Amendment, the
     performance by Borrower of its obligations hereunder and the consummation
     of the transactions contemplated hereby do not and will not conflict with
     any provision of law, statute, rule or regulation or of the certificate of
     incorporation and bylaws of Borrower, or of any material agreement,
     judgment, license, order or permit applicable to or binding upon Borrower,
     or result in the creation of any lien, charge or encumbrance upon any
     assets or properties of Borrower.  Except for those which have been
     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 Borrower of this Amendment or to consummate the
     transactions contemplated hereby.

          (d) When duly executed and delivered, each of this Amendment and the
     Loan Agreement will be a legal and binding obligation of Borrower,
     enforceable in accordance with its terms, except as limited by bankruptcy,
     insolvency or similar laws of general application relating to the
     enforcement of creditors' rights and by equitable principles of general
     application.

                                      -6-
<PAGE>
 
          (e) The unaudited quarterly Consolidated financial statements of
     Borrower dated as of September 30, 1995 fairly present Borrower's
     Consolidated financial position at such date and the Consolidated results
     of Borrower's operations and changes in Borrower's Consolidated cash flow
     for the period thereof.  Copies of such financial statements have
     heretofore been delivered to each Lender.  Since September 30, 1995, no
     material adverse change has occurred in the financial condition or
     businesses or in the Consolidated financial condition or businesses of
     Borrower.

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

     Section 5.1.  Consent to Amendment to Shelf Agreement.  Each Lender
                   ---------------------------------------              
consents and agrees that the Shelf Agreement as modified by the Second Amended
and Restated Master Shelf Agreement dated January 31, 1996 complies with the
provision of Section 5.2(b)(viii) of the Loan Agreement and each Lender further
consents to such modifications for purposes of Section 7.1(i) of the Loan
Agreement.

     Section 5.2.  Ratification of Agreements.  The Original Agreement as hereby
                   --------------------------                                   
amended and each other Loan Document affected hereby are ratified and confirmed
in all respects.  Any reference to the Loan Agreement in any Loan Document shall
be deemed to be a reference to the Original Agreement as hereby amended.  The
execution, delivery and effectiveness of this Amendment shall not, except as
expressly provided herein or therein, operate as a waiver of any right, power or
remedy of Agent or Lenders under the Loan Agreement, or any other Loan Document
nor constitute a waiver of any provision of the Loan Agreement, or any other
Loan Document.

     Section 5.3.  Survival of Agreements.  All representations, warranties,
                   ----------------------                                   
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loans, 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 Borrower or any Related
Person hereunder or under the Loan Agreement to any Lender shall be deemed to
constitute representations and warranties by, and/or agreements and covenants
of, Borrower under this Amendment and under the Loan Agreement.

                                      -7-
<PAGE>
 
     Section 5.4.  Loan Documents.  This Amendment is a Loan Document, and all
                   --------------                                             
provisions in the Loan Agreement pertaining to Loan Documents apply hereto.

     Section 5.5.  Governing Law.  This Amendment shall be governed by and
                   -------------                                          
construed in accordance with the laws of the State of Texas and any applicable
laws of the United States of America in all respects, including construction,
validity and performance.

     Section 5.6.  Counterparts.  This Amendment 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.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed as of the date first written above by their duly authorized officers.

                                   WESTERN GAS RESOURCES, INC.


                                   By:  /s/ John C. Walter
                                      ------------------------------------------
                                           John C. Walter
                                           Executive Vice President


                                   NATIONSBANK OF TEXAS, N.A.               
                                                                            
                                                                            
                                   By:  /s/ Michele L. Jones                
                                      ------------------------------------------
                                           Michele L. Jones                     
                                           Vice President                       
                                                                              
                                                                              
                                   BANKERS TRUST COMPANY          
                                   ----------------------         
                                                                              
                                                                              
                                   By:  /s/ Mary Jo Jolly         
                                      ------------------------------------------
                                           Mary Jo Jolly
                                           Assistant Vice President             

                                      -8-
<PAGE>
 
                                   BANK OF MONTREAL


                                   By:  /s/ Don Skipper
                                      ------------------------------------------
                                           Don Skipper
                                           Director


                                   CIBC INC.
                  

                                   By:  /s/ Gary C. Gaskill
                                      ------------------------------------------
                                           Gary C. Gaskill
                                           Vice President

                                      -9-
<PAGE>
 
           CONFIRMATION, ACKNOWLEDGEMENT AND CONSENT OF GUARANTORS


     Each of the undersigned (collectively "Guarantors") hereby (i) acknowledges
and consents to the foregoing Seventh Amendment to Third Restated Loan Agreement
(Term) of even date herewith by and among Western Gas Resources, Inc.,
NationsBank of Texas, N.A., as Agent ("Agent"), Bankers Trust Company, Bank of
Montreal, and CIBC Inc.; (ii) confirms the Restated Guaranty dated as of
September 2, 1994 executed by such Guarantor in favor of Agent and the Lenders
pursuant to the Original Agreement; and (iii) agrees that each of such
Guarantor's obligations and covenants with respect to such Restated Guaranty
shall remain in full force and effect after the execution of such Amendment.

     William J. Krysiak, Vice President-Finance of Western Gas Resources
Oklahoma, Inc., Western Gas Resources Texas, Inc., Western Gas Resources
Storage, Inc., Mountain Gas Resources, Inc., MGTC, Inc. and MIGC, Inc., is
executing this Confirmation, Acknowledgment and Consent of Guarantors in his
capacity of officer of each such corporation.

     Dated as of the 22nd day of March, 1996.

                            WESTERN GAS RESOURCES OKLAHOMA, INC.
                            WESTERN GAS RESOURCES TEXAS, INC.   
                            WESTERN GAS RESOURCES STORAGE, INC. 
                            MOUNTAIN GAS RESOURCES, INC.        
                            MGTC, INC.                          
                            MIGC, INC.                           



                            By:   /s/ William J. Krysiak
                               -------------------------------------------------
                                 William J. Krysiak, Vice President-Finance

                                      -11-