SECOND AMENDMENT
                                        TO
                  REVOLVING CREDIT AND LETTER OF CREDIT AGREEMENT

     This Amendment, dated as of April 30, 1993, is entered into by (1)
FRONTIER OIL AND REFINING COMPANY, a Delaware corporation (the "Borrower"), (2)
the banks parties to the Credit Agreement referred to below (the "Banks") and
(3) 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 (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, among other things, extend the Commitment Termination Date to
April 2, 1995 and, accordingly, hereby agree as set forth below.

     Section 1.   Amendments to Credit Agreement. 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, 1995; provided,
     however, that, upon (a) written request by the Borrower not later than May
     15, 1994 and (b) notice of such extension by the Agent to the Borrower not
     later than July 15, 1994, 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 2.4(a) of the Credit Agreement is amended by adding at
the end thereof a new sentence to read as follows:

     "Notwithstanding the provisions of the first sentence of this Section
     2.4(a), if the Borrower gives the Agent notice of a Borrowing consisting
     of Reference Rate Loans not later than 8:30 a.m., Los Angeles time, on
     the day of the proposed Borrowing, the Agent and the Banks will use their
     best efforts (but shall not be obligated) to make such Reference Rate
     Loans available on the day on which such notice is given; provided,
     however, that the Agent and the Banks shall no longer be required to use
     their best efforts as described in this sentence if the Agent, at its
     sole option exercisable at any time, gives the Borrower notice of the
     same."
          (c)  Section 2.12(a) of the Credit Agreement is amended in full to
read as follows:

               "(a) The Borrower shall pay to the Agent for the account of the
          Banks, from the Closing Date to the Commitment Termination Date, a
          letter of credit fee at the rate of one and one-half percent (1.50%)
          per annum on the aggregate of the average daily Letter of Credit
          Amounts of all Letters of Credit outstanding from time to time. Such
          letter of credit fee shall be payable monthly in arrears on the
          first Business Day of each calendar month, commencing on June 1,
          1993, to the extent accrued during the immediately preceding
          calendar month."

          (d)  Section 6.1(a) of the Credit Agreement is amended by adding the
following new proviso at the end thereof:

     "and further provided, however, that at least one Borrowing Base
     Certificate delivered during each calendar month for which an Inventory
     Audit is not conducted pursuant to Section 6.2 shall include a
     certification by the Borrower's chief financial officer or by the manager
     of the Cheyenne refinery to the effect that that portion of the quantity
     of Inventory set forth in such Borrowing Base Certificate that represents
     Inventory located at the Borrower's Cheyenne refinery was determined by
     the Borrower's measurement of the physical properties and volumes of such
     Inventory, using standard practices and standard tank-gauging wire-line
     devices."

     Section 2.  Conditions to Effectiveness. This Amendment shall become
effective as of the date first set forth above when the Agent has received (a)
an extension fee of $210,000 for the account of the Banks and (b) all of the
following documents, each (unless otherwise indicated) dated the date hereof,
in form and substance satisfactory to the Agent and in the number of originals
requested by the Agent:

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

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

               (iii) an amended and restated Agent's Fee Letter, duly executed
          by the Borrower;

               (iv) the Agent's form of General Environmental Questions for
          Non-Real Estate Secured Loans, duly completed and executed by the
          Borrower;

               (v) copies of the resolutions of the Board of Directors of the
          Borrower and each Guarantor approving this Amendment and the
          documents delivered pursuant hereto, certified by the Secretary or
          an Assistant Secretary of the Borrower or such Guarantor, as the
          case may be, 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;
               (vi) a certificate of the Secretary or an Assistant Secretary
          of the Borrower and each Affiliate as to the incumbency, and setting
          forth a specimen signature, of each of the persons who has signed
          this Amendment or any document delivered pursuant hereto;

               (vii) a certificate of the Borrower, signed on behalf of the
          Borrower by its President or a 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;

               (viii) recently dated good-standing certificates with respect
          to the Borrower, from the Secretaries of State of Colorado, Delaware
          and Wyoming; and

               (ix) 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, 1992 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,
fairly present the consolidated financial condition of FOC and its
Subsidiaries as of such date and the consolidated results of the operations of
FOC and its Subsidiaries for the fiscal year ended on such date, all in
accordance with generally accepted accounting principles applied on a
consistent basis. Since December 31, 1992 there has been no material adverse
change in the business, condition (financial or otherwise), operations,
performance, properties or prospects of FOC or any of its Subsidiaries. FOC
and its Subsidiaries have no material contingent liabilities except as
disclosed in such consolidated balance sheet 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," thereof," "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," "thereof," "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 Amendment.

     (b) Except as specifically amended above and except for the amendment and
restatement of the Agent's Fee Letter, 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. In addition, the Borrower shall pay any and all stamp and
other taxes payable or determined to be payable in connection with the
execution and delivery of this Amendment and the other instruments and
documents to be delivered hereunder, and the Borrower agrees to save the Agent
and each Bank harmless from and against any and all liabilities with respect
to or resulting from any delay in paying or omission to pay such taxes.

     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.  Wainoco Resolutions. Within six months of the date hereof,
the Borrower shall provide to the Agent, in form and substance satisfactory
thereto and in the number of originals requested thereby, copies of ratifying
resolutions of the Board of Directors of Wainoco approving this Amendment and
the consent signed by Wainoco with respect hereto, certified by the Secretary
or an Assistant Secretary of Wainoco to be correct and complete and in full
force and effect.

     Section 8.  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
                                   Vice President and Chief Financial Officer

                                   UNION BANK, as Agent and as a Bank

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

                                   By: /s/ Philip B. Flynn
                                   Name: PHILIP B. FLYNN
                                   Title: Senior Vice President