July 1, 1995



Frontier Oil Corporation
1700 Lincoln, Suite 2100
Denver, Colorado 80203

Attention:  Mr. Jon D. Galvin
            Vice President and Chief Financial Officer

Re:  Fourth Amendment to Guaranty

Gentlemen:

     We refer to the Guaranty made by Frontier Oil Corporation
(the "Guarantor") as of August 18, 1992, as amended by a First
Amendment to Guaranty dated as of October 8, 1992, a letter of
waiver and amendment dated March 17, 1993, a Second Amendment to
Guaranty dated as of December 31, 1993 and a Third Amendment to
Guaranty dated July 6, 1994 (said Guaranty, as so amended, herein
called the "Guaranty"), in favor of (1) Union Bank, Banque
Paribas and Den norske Bank AS (the "Banks") and (2) Union Bank,
as agent (the "Agent") for the Banks.  Unless otherwise defined
herein, terms defined in or pursuant to the Guaranty are used
herein as therein defined.

     The Guarantor has requested that Section 7.2(k) of the
Guaranty (concerning liquidity coverage) be amended as set forth
below, and the Banks are willing to do so.  Accordingly, the
parties hereby agree that, effective as of May 1, 1995, Section
7.2(k) of the Guaranty is amended in full to read as follows:

          "(k) Maintenance of Liquidity Coverage Ratio.  The
Guarantor will not permit the consolidated Liquidity Coverage
Ratio of it and its Subsidiaries as of the end of any calendar
month to be less than 1.08 to 1.0."

     On and after the effective date of this letter amendment,
each reference in the Guaranty to "this Guaranty," "hereunder,"
"hereof," "herein" or words of like import referring to the
Guaranty, and each reference in the other Credit Documents to
"the FOC Guaranty," "thereunder," "thereof," "therein" or words
of like import referring to the Guaranty, shall mean and be a
reference to the Guaranty as amended by this letter amendment. 
The Guaranty, as amended by this letter amendment, is and shall
continue to be in full force and effect and is hereby ratified
and confirmed in all respects.

     This letter amendment may be executed in any number of
counterparts and by any combination of the parties hereto in
separate counterparts, each of which counterparts shall be an
original and all of which taken together shall constitute one and
the same letter amendment.

     If you agree to the terms and provisions hereof, please
evidence your agreement by executing and returning five
counterparts of this letter amendment to the Agent.  This letter
amendment shall become effective as described above when it has
been executed and delivered by all of the parties hereto and when
the Agent has received the following documents from the
Guarantor, in form and substance satisfactory to the Agent:  (1)
copies of the resolutions of the Board of Directors of the
Guarantor approving this letter amendment and any documents
delivered by the Guarantor in connection herewith, 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 letter
amendment; and (2) 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 letter amendment or any document delivered by the Guarantor
in connection herewith.

Very truly yours,

UNION BANK, as Agent and as a Bank


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

Agreed as of the date first written above:

FRONTIER OIL CORPORATION

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


BANQUE PARIBAS

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


By:  /s/ Barton D. Schouest
- -------------------------------
Name:  Barton D. Schouest
Title:  Group Vice President


DEN NORSKE BANK AS


By:  /s/ Theodore S. Jadick, Jr.
- -------------------------------
Name:  Theodore S. Jadick, Jr.
Title:  Senior Vice President


By:  /s/ Fran Meyers
- -------------------------------
Name:  Fran Meyers
Title:  Vice President