July 6, 1994



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

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

Re:  Third 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 and a Second Amendment
to Guaranty dated as of December 31, 1993 (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 Banks wish to establish limitations on capital
expenditures by the Guarantor and its Subsidiaries for calendar
year 1994 and subsequent years.  Accordingly, the parties hereby
agree that, effective as of the date first set forth above,
Section 7.2(j) of the Guaranty is amended in full to read as
follows:

          "(j) Capital Expenditures.  The Guarantor will not
make, or permit any of its Subsidiaries to make, any expenditure
for fixed or capital assets that would cause the aggregate of all
such expenditures made by the Guarantor and its Subsidiaries to
exceed $15,000,000 in any calendar year, commencing with calendar
year 1994."

     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 of the date first set forth
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


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


By:  /s/ J. Wehner
- ------------------------------
Name:  J. Wehner
Title:  Senior Vice President


DEN NORSKE BANK AS


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


By:  /s/ Jairo Jimenez
- ------------------------------
Name:  Jairo Jimenez
Title:  Assistant Treasurer