SIXTH AMENDMENT
                               TO
        REVOLVING CREDIT AND LETTER OF CREDIT AGREEMENT
                                

     This Sixth Amendment to Revolving Credit and Letter of Credit Agreement
(this "Amendment"), dated as of July 1, 1996, is entered into by (1) FRONTIER
OIL AND REFINING COMPANY, a Delaware corporation (the "Borrower"), (2) the bank
parties to the Credit Agreement referred to below (the "Banks") and (3) UNION
BANK OF CALIFORNIA, N.A.., a national banking association (successor in
interest to Union Bank, a California banking corporation), as agent (the
"Agent") for the Banks.

                            Recitals

     A.   The Borrower, the Banks and the Agent have entered into a Revolving
Credit and Letter of Credit Agreement dated as of August 10, 1992, as amended
by a letter of waiver and amendment dated March 17, 1993, a Second Amendment to
Revolving Credit and Letter of Credit Agreement dated as of April 30, 1993, a
Third Amendment to Revolving Credit and Letter of Credit Agreement dated as of
December 31, 1993, a Fourth Amendment to Revolving Credit and Letter of Credit
Agreement dated as of July 6, 1994 and a Fifth Amendment to Revolving Credit
and Letter of Credit Agreement dated as of July 1, 1995 (said Agreement, as so
amended, herein called the "Credit Agreement"). Terms defined in the Credit
Agreement and not otherwise defined herein have the same respective meanings
when used herein, and the rules of interpretation set forth in Sections 1.2 and
1.3 of the Credit Agreement are incorporated herein by reference.

     B.   The Borrower, the Banks and the Agent wish to amend the credit
Agreement to extend the Commitment Termination Date and change certain pricing
terms thereunder. Accordingly, the Borrower, the Banks and the Agent hereby
agree as set forth below.

     Section 1. Amendments to Credit Agreement. Effective as of the date first
set forth above and subject to satisfaction of the conditions precedent set
forth in Section 2, the Credit Agreement is hereby amended as follows:

          (a)  The definition of  "Commitment Termination Date" in Section 1.1
of the Credit Agreement is amended in full to read as follows:

          " 'Commitment Termination Date' means April 2, 1998; provided,
          however, that, upon (a) written request by the Borrower not later
          than May 15, 1997 and (b) notice of such extension by the Agent to
          the Borrower not later than July 15, 1997, the Commitment Termination
          Date may be extended by the Agent and the Banks, in their sole and
          absolute discretion, for up to an additional year; and further
          provided, however, that the Agent's failure to notify the Borrower of
          any such extension by the applicable date referred to above shall
          constitute a denial of such extension."

          (b)  Section 2.2 (a) of the Credit Agreement is amended by deleting
the words and figures "four-tenths percent (0.4%)" and substituting the words
and figures "three hundred seventy-five thousandths percent (.375%)."

          (c)  Section 2.6(a) of the Credit Agreement is amended by deleting
the words and figures "seven-eighths percent (0.875%)" in clause (i) thereof
and "two percent (2.00%)" in clause (ii) thereof and substituting the words and
figures "(one-half percent (0.5%)" and "one and three-quarters percent
(1.75%)," respectively.

     Section 2. Conditions to Effectiveness . This Amendment shall become
effective as of the date first set forth above when the Agent has received a
renewal fee of $100,000 for the account of the Banks and all of the following
documents, each dated on or before the date hereof, in form and substance
satisfactory to the Agent and in the number of originals requested by the
Agent:

          (a)  this Amendment, duly executed by the Borrower and the Banks;

          (b)  an amendment to the FOC Guaranty for the purpose of amending
Schedule 2 thereto, duly executed by FOC and the Banks, together with the other
documents required to be delivered to the Agent as conditions precedent to the
effectiveness of such amendment;

          (c)  an amendment and restatement of the Agent's Fee Letter;

          (d)  a consent to this Amendment, duly executed by Wainoco and the
Guarantors;

          (e)  copies of the resolutions of the Board of Directors of the
Borrower approving this Agreement and any documents delivered by the Borrower
pursuant hereto, certified by the Secretary or an Assistant Secretary of the
Borrower to be correct and complete and in full force and effect as of the date
of execution, and as of the effective date, of this Amendment;

          (f)  a certificate of the Secretary of Assistant Secretary of the
Borrower as to the incumbency, and setting forth a specimen signature, of each
of the persons who has signed this Amendment or any document delivered by the
Borrower pursuant hereto;

          (g)  a certificate of the Borrower, signed on behalf of the Borrower
by its President or Vice President and its Secretary or any Assistant
Secretary, certifying as to (A) the absence of any amendments to the charter
documents or bylaws of the Borrower on or after August 18, 1992, (B) the
truthfulness in all material respects of the representations and warranties
contained in the Credit Documents as though made on and as of the effective
date of this Amendment and (C) the absence of any event occurring and
continuing, or resulting from the effectiveness of this Amendment, that
constitutes a Default or an Event of Default; and

          (h)  such other approvals, opinions and documents as the Agent may
reasonably request.

     Section 3. Representations and Warranties of Borrower. The Borrower
represents and warrants as follows:

          (a)  The Borrower is a corporation duly organized, validly existing
and in good standing under the laws of the State of Delaware.

          (b)  The execution, delivery and performance by the Borrower of this
Amendment and the Credit Documents, as amended hereby, to which it is or is to
be a party are within the Borrower's corporate powers, have been duly
authorized by all necessary corporate action and do not (i) contravene the
Borrower's charter documents or bylaws, (ii) contravene any Governmental Rule
or contractual restriction binding on or affecting the Borrower or (iii) result
in or require the creation or imposition of any Lien or preferential
arrangement of any nature (other than any created by the Credit Documents) upon
or with respect to any of the properties now owned or hereafter acquired by the
Borrower.

          (c)  No Governmental Action is required for the due execution,
delivery or performance by the Borrower of this Amendment or any of the Credit
Documents, as amended hereby, to which the Borrower is or is to be a party.

          (d)  This Amendment and each of the Credit Documents, as amended
hereby, to which the Borrower is a party constitute legal, valid and binding
obligations of the Borrower enforceable against the Borrower in accordance with
their respective terms.

          (e)  The Security Agreement, the Account Pledge Agreement and the
Note Pledge Agreement constitute valid and perfected first-priority Liens on
the Collateral covered thereby, enforceable against all third parties in all
jurisdictions, and secure the payment of all obligations of the Borrower under
the Credit Documents, as amended hereby; and the execution, delivery and
performance of this Amendment do not adversely affect the Lien of the Security
Agreement, the Account Pledge Agreement or the Note Pledge Agreement.

          (f)  The consolidated balance sheet of FOC and its Subsidiaries as of
December 31, 1995 and the related consolidated statements of income, retained
earnings and cash flows of FOC and its Subsidiaries for the fiscal year then
ended, certified by Arthur Andersen & Co., independent public accountants, and
the report as of May 31, 1996 referred to in Section 7.1(j)(i) of the FOC
Guaranty, certified by the chief financial officer or chief accounting officer
of FOC, fairly present the consolidated financial condition of FOC and its
Subsidiaries as of such dates and the consolidated results of the operations of
FOC and its Subsidiaries for the fiscal periods ended on such dates, all in
accordance with generally accepted accounting principles applied on a
consistent basis. Since May 31, 1996 there has been no material adverse change
in the business, condition (financial or otherwise), operations, performance,
properties or prospects of material contingent liabilities except as disclosed
in such financial statements or the notes thereto.

          (g)  There is no pending or, to the knowledge of the Borrower,
threatened action or proceeding affecting FOC or any its Subsidiaries before
any Governmental Person or arbitrator that may materially and adversely affect
the financial condition or operations of FOC or any of its Subsidiaries or that
purports to affect the legality, validity or enforceability of this Amendment
or any of the Credit Documents, as amended hereby.

     Section 4. Reference to and Effect on Credit Documents.

     (a)  On and after the effective date of this Amendment, each reference in
the Credit Agreement to "this Agreement," "hereunder," "hereof," "herein" or
any other expression of like import referring to the Credit Agreement, and each
reference in the other Credit Documents to "the Credit Agreement,"
"thereunder," "therein" or any other expression of like import referring to the
Credit Agreement, shall mean and be a reference to the Credit Agreement as
amended by this Agreement.

     (b)  Except as specifically amended or referred to above, the Credit
Agreement and the other Credit Documents shall remain in full force and effect
and are hereby ratified and confirmed. Without limiting the generality of the
foregoing, the Security Agreement, the Account Pledge Agreement and the Note
Pledge Agreement, and all of the Collateral described therein, do and shall
continue to secure the payment of all obligations of the Borrower under the
Credit Documents, as amended hereby.

     (c)  The execution, delivery and effectiveness of this Amendment shall
not, except as expressly provided herein, operate as a waiver of any right,
power or remedy of any Bank or the Agent under any of the Credit Documents or
constitute a waiver of any provision of any of the Credit Documents.

     Section 5.  Costs, Expenses and Taxes. The Borrower agrees to pay on
demand all costs and expenses of the Agent in connection with the preparation,
execution and delivery of this Amendment and the other instruments and
documents to be delivered hereunder, including the reasonable fees and
out-of-pocket expenses of counsel for the Agent with respect thereto and with
respect to advising the Agent as to its rights and responsibilities hereunder
and thereunder.

     Section 6. Execution in Counterparts. This Amendment may be executed in
any number of counterparts and by the parties hereto in separate counterparts,
each of which when so executed and delivered shall be deemed to be an original
and all of which taken together shall constitute one and the same instrument.

     Section 7. Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF CALIFORNIA APPLICABLE TO
CONTRACTS MADE AND PERFORMED IN THE STATE OF CALIFORNIA.


                              FRONTIER OIL AND REFINING COMPANY



                              By:  /s/ Jon D. Galvin
                                   Jon D. Galvin
                                   Vice President and Chief Financial Officer

                              UNION BANK OF CALIFORNIA, N.A.,
                                  As Agent and as a Bank


                              By:  /s/ Richard P. DeGrey, Jr.
                                   Richard P. DeGrey, Jr.
                                   Vice President

                              BANQUE PARIBAS


                              By:  /s/ Mark M. Green
                              Name:     Mark M. Green            
                              Title:    Vice President           



                              By:  /s/ Marian Livingston
                              Name:     Marian Livingston        
                              Title:    Vice President           

                              DEN NORSK BANK AS


                              By:  /s/ Byron L. Cooley
                              Name:     Byron L. Cooley          
                              Title:    First Vice President     



                              By:  /s/ William V. Moyer
                              Name:     William V. Moyer         
                              Title:    Vice President