Exhibit 10.1

FIRST AMENDMENT
TO
SECOND AMENDED AND RESTATED REVOLVING CREDIT AGREEMENT

This Amendment, dated as of February 3, 2006, is entered into by (1) FRONTIER
OIL AND REFINING COMPANY, a Delaware corporation (the “Borrower”), (2) FRONTIER
OIL CORPORATION, a Wyoming corporation (“FOC”), (3) each of the financial
institutions party to the Credit Agreement referred to below (the “Lenders”) and
(4) UNION BANK OF CALIFORNIA, N.A., a national banking association, as
administrative agent (the “Administrative Agent”) for the Lenders.

Recitals

A. The Borrower, FOC, the Lenders, the Administrative Agent and BNP Paribas, a
French banking corporation, as syndication agent, are party to a Second Amended
and Restated Revolving Credit Agreement dated as of November 22, 2004 (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 Section 1.3 of the Credit Agreement are
incorporated herein by reference.

B. The Borrower, FOC and the Lenders wish to amend the Credit Agreement to,
among other things, (1) revise the definition of “Cash Equivalents” and (2)
permit the Borrower and FOC to enter into certain transactions for the purpose
of financing the purchase of crude oil by the Borrower. Accordingly, for good
and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrower, FOC, the Lenders and the Administrative Agent hereby
agree as set forth below.

SECTION 1.  Amendments to Credit Agreement
. Effective as of the date hereof but subject to satisfaction of the conditions
precedent set forth in Section 2 of this Amendment, the Borrower, FOC and the
Lenders hereby agree as set forth below.

(a)  The definition of “Cash Equivalents” in Section 1.1 of the Credit Agreement
is amended in full to read as follows:

“‘Cash Equivalents’ means: (a) United States dollars or up to $2,000,000 of
Canadian dollars; (b) securities issued or directly and fully guaranteed or
insured by the United States government or any agency or instrumentality thereof
and having maturities of not more than six months from the date of acquisition;
(c) certificates of deposit and Eurodollar time deposits with maturities of one
year or less from the date of acquisition, bankers’ acceptances with maturities
not exceeding one year and overnight bank deposits, in each case with any
commercial bank organized under the laws of any country that is a member of the
Organization for Economic Cooperation and Development and having capital and
surplus in excess of $500,000,000; (d) repurchase obligations with a term of not
more than seven days for underlying securities of the types described in clauses
(b) and (c) above that are entered into with any financial institution meeting
the qualifications specified in clause (c) above; (e) commercial paper having
the highest rating obtainable from Moody’s or S&P and in each case maturing
within 180 days after the date of acquisition; (f) commercial paper, maturing
not more than 180 days after the date of acquisition, issued by a corporation
organized and existing under the laws of the United States of America or any
foreign country recognized by the United States of America, with a rating at the
time as of which any investment therein is made of P-1 (or higher) according to
Moody’s or A-1 (or higher) according to S&P; (g) deposits available for
withdrawal on demand with any commercial bank not meeting the qualifications
specified in clause (c) above, provided that all such deposits do not exceed
$2,000,000 in the aggregate at any one time; and (h) money market mutual funds
substantially all of the assets of which are of the types described in the
preceding clauses (a) through (f).”

(b)  Section 1.1 of the Credit Agreement is amended by adding the following new
defined term in appropriate alphabetical order:

“‘Utexam Transactions’ means the crude oil purchases and related transactions
contemplated by the Master Crude Oil Purchase and Sale Contract dated February
3, 2006 by and among Utexam Ltd., a corporation organized under the laws of the
Republic of Ireland, as seller, the Borrower, as purchaser, and FOC, as
guarantor.”

(c)  Section 7.4 of the Credit Agreement is amended by deleting the word “and”
at the end of clause (i), deleting the period at the end of clause (j) and
substituting “; and” and adding the following new clause (k) after clause (j):

“(k) the obligations of the Borrower, as purchaser, and FOC, as guarantor, in
respect of the Utexam Transactions, provided that such obligations do not
exceed, at any time outstanding, the sum of $150,000,000 plus the amount of any
related transportation costs and expenses.”

(d)  Schedule 5 to the Credit Agreement is amended by deleting the reference to
FGI, LLC, its owner and the related ownership percentage.

SECTION 2.  Conditions Precedent
. This Amendment shall become effective as of the date first set forth above
when and if the Administrative Agent receives all of the following, each dated
the date hereof, in form and substance satisfactory to the Administrative Agent
and in the number of originals requested thereby:

(a)  this Amendment, duly executed by the Borrower, FOC and the Majority
Lenders; and

(b)  a consent to this Amendment, duly executed by the Guarantors.

SECTION 3.  Representations and Warranties
. Each of the Borrower and FOC represents and warrants to the Lenders and the
Administrative Agent as set forth below.

(a)  The execution, delivery and performance by each of the Borrower and FOC of
this Amendment and the Credit Agreement, as amended hereby, and the consummation
of the transactions contemplated hereby and thereby, are within such Credit
Party’s legal powers, have been duly authorized by all necessary legal action
and do not (i) contravene such Credit Party’s charter or bylaws, (ii) violate
any Governmental Rule, (iii) conflict with or result in the breach of, or
constitute a default under, any Material Contract, loan agreement, indenture,
mortgage, deed of trust or lease, or any other contract or instrument, binding
on or affecting such Credit Party, any of its Subsidiaries or any of their
respective properties, the conflict, breach or default of which could reasonably
be expected to have a Material Adverse Effect, or (iv) result in or require the
creation or imposition of any Lien upon or with respect to any of the properties
of such Credit Party or any of its Subsidiaries, except for Liens created under
the Credit Documents. Neither such Credit Party nor any of its Subsidiaries is
in violation of any Governmental Rule or in breach of any such contract, loan
agreement, indenture, mortgage, deed of trust, lease or other contract or
instrument, the violation or breach of which could reasonably be expected to
have a Material Adverse Effect.

(b)  No Governmental Action, and no authorization, approval or other action by,
or notice to, any third party, is required for the due execution, delivery or
performance by the Borrower or FOC of this Amendment or the Credit Agreement, as
amended hereby, or for the consummation of the transactions contemplated hereby
or thereby, except for (i) authorizations, approvals and other actions by, and
notices to, third parties, the failure to obtain which could not reasonably be
expected to have a Material Adverse Effect, and (ii) Governmental Action that
has been duly obtained, taken, given or made and is in full force and effect.

(c)  This Amendment and the Credit Agreement, as amended hereby, have been duly
executed and delivered by the Borrower and FOC. This Amendment and the Credit
Agreement, as amended hereby, are the legal, valid and binding obligations of
the Borrower and FOC, enforceable against each such Credit Party in accordance
with their respective terms, except as the enforceability hereof or thereof may
be limited by bankruptcy, insolvency, moratorium, reorganization or other
similar laws affecting creditors’ rights generally or by equitable principles
relating to enforceability.

(d)  Each of the Security Agreement and the Stock Pledge Agreement constitutes a
valid and perfected first-priority Lien on the Collateral purported to be
encumbered thereby, enforceable against all third parties in all jurisdictions,
and secures the payment of all obligations of the Borrower or FRMI, as
applicable, under the Credit Documents, as amended hereby, to which the Borrower
or FRMI, as applicable, is a party, and the execution, delivery and performance
of this Amendment do not adversely affect the Lien of the Security Agreement or
the Stock Pledge Agreement.

(e)  There has been no amendment to the charter documents or bylaws of the
Borrower on or after November 5, 2004 or of FOC on or after November 8, 2004.
The representations and warranties contained in each Credit Document, as amended
hereby, to which the Borrower and/or FOC is a party are correct in all material
respects on and as of the date hereof, before and after giving effect to this
Amendment, as though made on and as of the date hereof. No event has occurred
and is continuing, or would result from the effectiveness of this Amendment,
that constitutes a Default.

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 words
of like import referring to the Credit Agreement, and each reference in the
other Credit Documents to “the Credit Agreement,” “thereunder,” “thereof,”
“therein” or words 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, 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 and the Stock Pledge Agreement and all of the Collateral described
therein do and shall continue to secure the payment of all obligations stated to
be secured thereby under the Credit Documents, as amended hereby.

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

SECTION 5.  Costs and Expenses
. The Borrower agrees to pay on demand all costs and expenses of the
Administrative 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 Administrative Agent with respect thereto and with respect to advising
the Administrative 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 agreement. Delivery of an executed counterpart
of a signature page to this Amendment by telecopier shall be effective as
delivery of a originally executed counterpart of this Amendment.
 
SECTION 7.  Governing Law
. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED AND ENFORCED IN ACCORDANCE
WITH, THE LAWS OF THE STATE OF CALIFORNIA APPLICABLE TO CONTRACTS MADE AND
PERFORMED IN THE STATE OF CALIFORNIA.
 

 
The parties hereto have caused this Amendment to be executed by their respective
duly authorized representatives as of the date first written above.

FRONTIER OIL AND REFINING COMPANY

By:  /s/ Leo J. Hoonakker   
Leo J. Hoonakker
Vice President and Treasurer

FRONTIER OIL CORPORATION

By:  /s/ Doug Aron   
Name:   Doug Aron   
Title:   VP—Corporate Finance 

UNION BANK OF CALIFORNIA, N.A.,
as Administrative Agent and a Lender

By:  /s/ Sean Murphy  
Name:   Sean Murphy   
Title:  Vice President   

BNP PARIBAS

By:  /s/ Douglas R. Liftman 
Name:   Douglas R. Liftman  
Title:  Managing Director  

By:  /s/ Polly Schott  
Name:   Polly Schott   
Title:  Vice President   

TORONTO DOMINION (TEXAS), INC.

By:  /s/ Jackie Barrett  
Name:   Jackie Barrett  
Title:  Authorized Signatory  

WELLS FARGO BANK, N.A.

By:  /s/ Art Krasny   
Name:   Art Krasny   
Title:  Relationship Manager  

BANK OF SCOTLAND

By:  /s/ Karen Weich  
Name:   Karen Weich   
Title:  Assistant Vice President 

U.S. BANK NATIONAL ASSOCIATION

By:  /s/ Mark E. Thompson  
Name:   Mark E. Thompson  
Title:  Vice President   

THE FROST NATIONAL BANK

By:  /s/ Thomas H. Dungan 
Name:   Thomas H. Dungan  
Title:  Sr. Vice President  

HIBERNIA NATIONAL BANK

By:  /s/ Corwin Dupree  
Name:   Corwin Dupree  
Title:  Vice-President