SECOND AMENDMENT TO GUARANTY



     This Amendment, dated as of December 31, 1993, is entered
into by (1) FRONTIER OIL CORPORATION, a Delaware corporation (the
"Guarantor"), (2) the banks (the "Banks") parties to the Credit
Agreement (as hereinafter defined) and (3) UNION BANK, a
California banking corporation, as agent (the "Agent") for the
Banks.

                                 Recitals

     A.  Frontier Oil and Refining Company, a Delaware
corporation (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 and a Second Amendment to
Revolving Credit and Letter of Credit Agreement dated as of April
30, 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 Guarantor has executed a Guaranty dated as of August
18, 1992, as amended by a First Amendment to Guaranty dated as of
October 8, 1992 and a letter of waiver and amendment dated March
17, 1993 (said Guaranty, as so amended, herein called the
"Guaranty"), in favor of the Banks and the Agent, guaranteeing
all of the obligations of the Borrower under the Credit Agreement
and the other Credit Documents.

     C.  The Banks, the Agent and the Guarantor wish (1) to amend
the Guaranty to change the terms of certain of the covenants
contained therein and (2) to provide for the temporary waiver of
the requirements of another such covenant, and they accordingly
thereby agree as set forth below.

     Section 1.  Amendments to Guaranty.  Effective as of
November 23, 1993 and subject to satisfaction of the conditions
precedent set forth in Section 2, the Guaranty is hereby amended
as follows:

          (a)  Section 7.2(b) of the Guaranty is amended by
deleting the word "and" at the end of subsection (iv), deleting
the period at the end of subsection (v) and substituting "; and"
and adding the following new subsection (vi):

              "(vi)  the guaranty by the Guarantor of the
obligations of FRI to Indeck Power Equipment Company under the
Lease dated November 23, 1993 between those two parties,
concerning the lease of two steam boilers."

          (b)  Section 7.2(c) of the Guaranty is amended by
deleting the figure "$3,000,000" therein and substituting the
figure "$8,000,000."

          (c)  Section 7.2(j) of the Guaranty is amended by
deleting the figure "$25,000,000" therein and substituting the
figure "$30,000,000."

     Section 2.  Conditions to Effectiveness.  This Amendment
shall become effective when the Agent has received all of the
following documents, each dated 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 Guarantor and
the Banks;

          (b)  a consent to this Amendment duly executed by
Wainoco and the Guarantors other than Frontier Oil Corporation;

          (c)  copies of the resolutions of the Board of
Directors of the Guarantor approving this Amendment and any
documents delivered by the Guarantor pursuant hereto, certified
by the Secretary or an Assistant Secretary of the Guarantor 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;

          (d)  a certificate of the Secretary or an Assistant
Secretary of the Guarantor 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 Guarantor
pursuant hereto;

          (e)  a certificate of the Guarantor, signed on behalf
of the Guarantor 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 Guarantor 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

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

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

          (a)  The Guarantor 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
Guarantor of this Amendment and the Credit Documents, as amended
hereby, to which it is or is to be a party are within the
Guarantor's corporate powers, have been duly authorized by all
necessary corporate action and do not (i) contravene the
Guarantor's charter documents or bylaws, (ii) contravene any
Governmental Rule or contractual restriction binding on or
affecting the Guarantor 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 Guarantor.

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

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

          (e)  The Stock Pledge Agreement constitutes a valid and
perfected a first-priority Lien on the Collateral covered
thereby, enforceable against all third parties in all
jurisdictions, and secures the payment of all obligations of the
Guarantor under the Guaranty, as amended hereby; and the
execution, delivery and performance of this Amendment do not
adversely affect the Lien of the Stock Pledge Agreement.

          (f)  The consolidated balance sheet of the Guarantor
and its Subsidiaries as of December 31, 1992 and the related
consolidated statements of income, retained earnings and cash
flows of the Guarantor and its Subsidiaries for the fiscal year
then ended, certified by Arthur Andersen & Co., independent
public accountants, and the report as of October 31, 1993
referred to in Section 7.1(j) (i) of the Guaranty, certified by
the chief financial officer or chief accounting officer of the
Guarantor, fairly present the consolidated financial condition of
the Guarantor and its Subsidiaries as of such dates and the
consolidated results of the operations of the Guarantor 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 October 31, 1993 there has been no
material adverse change in the business, condition (financial or
otherwise), operations, performance, properties or prospects of
the Guarantor or any of its Subsidiaries.  The Guarantor and its
Subsidiaries have no 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
Guarantor, threatened action or proceeding affecting the
Guarantor or any its Subsidiaries before any Governmental Person
or arbitrator that may materially and adversely affect the
financial condition or operations of the Guarantor or any of its
Subsidiaries or that purports to affect the legality, validity or
enforceability of this Amendment or any of the other Credit
Documents, as amended hereby, to which the Guarantor is a party.

     Section 4.  Waiver.  The Banks hereby waive the requirements
of Section 7.2(a) of the Guaranty during the period from December
31, 1993 to June 30, 1994, but only to the extent that such
requirements are violated by Liens now existing in favor of Petro
Engineering and Construction, Inc. and certain union workers, as
disclosed in the letter dated December 10, 1993 from Jon D.
Galvin of the Guarantor to Richard P. DeGrey, Jr. of the Agent,
copies of which letter (including attachments) have been
delivered to the Banks.  The effectiveness of this waiver is
conditioned upon the accuracy of the information contained in the
aforementioned letter (including attachments), and any material
adverse change or material inaccuracy in such information shall
cause this waiver to be of no further force or effect.

     Section 5.  Reference to and Effect on Credit Documents.

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

          (b)  Except as specifically amended above and except
for an amendment to the Credit Agreement entered into
simultaneously herewith, the Guaranty 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 Stock Pledge Agreement and all of the Collateral
described therein do and shall continue to secure the payment of
all obligations of the Guarantor under the Guaranty, 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 6.  Costs, Expenses and Taxes.  The Guarantor 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
Guarantor 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 Guarantor 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 7.  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 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 CORPORATION


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


UNION BANK, as Agent and as a Bank


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


By:  /s/ Walter M. Roth
- -------------------------
Name:  Walter M. Roth
Title:  Vice President


BANQUE PARIBAS

By:  /s/ Edward K. Chin
- -------------------------
Name:  Edward K. Chin
Title:  Vice President


By:  /s/ Philippe De Gentile
- -------------------------
Name:  Philippe De Gentile
Title:  DGM


DEN NORSKE BANK AS


By:  /s/ Nelvin Farstad
- -------------------------
Name:  Nelvin Farstad
Title:  Senior Vice President, New York Branch


By:  /s/ Philip F. Kurpiewski
- -------------------------
Name:  Philip F. Kurpiewski
Title:  Vice President, New York Branch