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Exhibit 10.9.4

SIXTH MODIFICATION AGREEMENT

BY THIS SIXTH MODIFICATION AGREEMENT (the "Agreement"), made and entered into as
of the 13th day of May, 2004, WELLS FARGO BANK, NATIONAL ASSOCIATION, as
administrative agent (the "Administrative Agent") for the Banks listed in the
hereinafter defined Credit Agreement (the "Banks") and as the Issuing Bank and
the Swing Line Lender, and KNIGHT TRANSPORTATION, INC., an Arizona corporation
(the "Company") and all present and future Significant Subsidiaries of the
Company (with the Company, the "Borrower"), in consideration of the mutual
covenants herein contained and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, hereby confirm and
agree as follows:

SECTION 1.     RECITALS; ACKNOWLEDGEMENTS.

1.1     The Borrower and the Administrative Agent and the Banks entered into
that Credit Agreement dated April 6, 2001 (as amended from time to time, the
"Credit Agreement") to provide financial accommodations to the Borrower as
provided therein. The Credit Agreement was previously amended by that
Modification Agreement dated as of June 5, 2001, that Second Modification
Agreement dated as of November 19, 2001, that Third Modification Agreement dated
as of February 13, 2003, that Fourth Modification Agreement dated as of
September 15, 2003 and that Fifth Modification Agreement dated as of December
15, 2003.
 
1.2     Borrower and the Administrative Agent, with the consent of the Banks,
desire to modify the Credit Agreement as set forth herein.

1.3     All undefined capitalized terms used herein shall have the meaning given
them in the Credit Agreement.

SECTION 2.    CREDIT AGREEMENT.
 
2.1     The following definitions in Section 1.1 of the Credit Agreement are
hereby amended to read as follows:

    "Letter of Credit Commitment" shall mean $11,000,000.00.

    "Maximum RLC Commitment" shall mean $11,000,000.00.

2.2     Schedule 2.1 of the Credit Agreement is hereby amended to read as
attached hereto.

2.3     All references in the Note to "10,000,000.00" or to "Ten Million and
NO/100 Dollars" are hereby amended to read "11,000,000.00" and "Eleven Million
and NO/100 Dollars," respectively.

SECTION 3.     OTHER MODIFICATIONS, RATIFICATIONS AND AGREEMENTS.

3.1     All references to the Credit Agreement in the other Loan Documents are
hereby amended to refer to the Credit Agreement as hereby amended.

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3.2     Borrower hereby reaffirms to the Banks each of the representations,
warranties, covenants and agreements of Borrower set forth in the Credit
Agreement, with the same force and effect as if each were separately stated
herein and made as of the date hereof.

3.3     Borrower hereby ratifies, reaffirms, acknowledges, and agrees that the
Notes and the Credit Agreement represent valid, enforceable and collectible
obligations of Borrower, and that there are no existing claims, defenses,
personal or otherwise, or rights of setoff whatsoever with respect to any of
these documents or instruments. Borrower further acknowledges and represents
that no event has occurred and no condition exists that, after notice or lapse
of time, or both, would constitute a default under this Agreement, the Notes or
the Credit Agreement.

3.4     All terms, conditions and provisions of the Credit Agreement are
continued in full force and effect and shall remain unaffected and unchanged
except as specifically amended hereby. The Credit Agreement, as amended hereby,
is hereby ratified and reaffirmed by Borrower, and Borrower specifically
acknowledges the validity and enforceability thereof.

SECTION 4.     GENERAL.
 
4.1     This Agreement in no way acts as a release or relinquishment of those
rights securing payment of the Loans. Such rights are hereby ratified,
confirmed, renewed and extended by Borrower in all respects.

4.2     The modifications contained herein shall not be binding upon the Banks
until the Administrative Agent shall have received all of the following:

 
(a)
An original of this Agreement fully executed by the Borrower.

 
(b)
Such resolutions or authorizations and such other documents as the
Administrative Agent may require relating to the existence and good standing of
the Borrower and the authority of any person executing this Agreement or other
documents on behalf of the Borrower.

4.3     Borrower shall execute and deliver such additional documents and do such
other acts as the Banks may reasonably require to fully implement the intent of
this Agreement.

4.4     Borrower shall pay all costs and expenses, including, but not limited
to, reasonable attorneys' fees incurred by the Administrative Agent in
connection herewith, whether or not all of the conditions described in Paragraph
4.2 above are satisfied. Banks, at their option, but without any obligation to
do so, may advance funds to pay any such costs and expenses that are the
obligation of the Borrower, and all such funds advanced shall bear interest at
the highest rate provided in the Notes and shall be due and payable upon demand.

4.5     Notwithstanding anything to the contrary contained herein or in any
other instrument executed by Borrower, the Administrative Agent or the Banks, or
in any other action or conduct undertaken by Borrower, the Administrative Agent
or the Banks on or before the date hereof, the agreements, covenants and
provisions contained herein shall constitute the only evidence of the Banks'
consent to modify the terms and provisions of the Credit Agreement. Accordingly,
no

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express or implied consent to any further modifications involving any of the
matters set forth in this Agreement or otherwise shall be inferred or implied by
the Banks' consent to this Agreement. Further, the Banks' consent to this
Agreement shall not constitute a waiver (either express or implied) of the
requirement that any further modification of the Credit Agreement shall require
the express written consent of the Bank; no such consent (either express or
implied) has been given as of the date hereof.

4.6     Time is hereby declared to be of the essence hereof of the Credit
Agreement, and Banks require, and Borrower agrees to, strict performance of each
and every covenant, condition, provision and agreement hereof, of the Credit
Agreement.

4.7     This Agreement shall be binding upon, and shall inure to the benefit of,
the parties hereto and their heirs, personal representatives, successors and
assigns.

4.8     This Agreement is made for the sole protection and benefit of the
parties hereto, and no other person or entity shall have any right of action
hereon.

4.9     This Agreement shall be governed by and construed according to the laws
of the State of Arizona.

    IN WITNESS WHEREOF, these presents are executed as of the date indicated
above.

 
WELLS FARGO BANK, NATIONAL ASSOCIATION
 
 
 
By:
 
 
/s/ Keri Tignini
 
Name:
Keri Tignini
 
Its:
Vice President
       
ADMINISTRATIVE AGENT
     
KNIGHT TRANSPORTATION, INC.
 
 
 
By:
 
 
/s/ Tim Kohl
 
Name:
Tim Kohl
 
Its:
Treasurer
     
QUAD-K LEASING, INC., an Arizona corporation
 
 
 
By:
 
 
/s/ Tim Kohl
 
Name:
Tim Kohl
 
Its:
President
       
BORROWER
           

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CONSENT OF THE BANKS

Re: Knight Transportation, Inc.

The following:

(a)     is a Bank named in that Credit Agreement dated April 6, 2001 between
Knight Transportation, Inc., an Arizona corporation (the "Company"), all present
and future Significant Subsidiaries of the Company (the "Borrower"), Wells Fargo
Bank, National Association, as administrative agent for the Banks (the
"Administrative Agent"), and the Banks; and

(b)     consents to that Sixth Modification Agreement dated May 13, 2004 entered
into between the Borrower and the Administrative Agent.

 
WELLS FARGO BANK, NATIONAL ASSOCIATION
 
 
 
By:
 
 
/s/ Keri Tignini
 
Name:
Keri Tignini
 
Its:
Vice President
       
"Bank"

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SCHEDULE 2.1

COMMITMENTS OF BANKS
as to the Facility
as of ___________, 2004

   
                 Bank
  %   
$
                 
1.
   
Wells Fargo Bank,
National Association
   
100%
 
 
$11,000,000.00
 
 
 
   
 
Maximum RLC
Commitment 
   
100%
 
 
$11,000,000.00
 

Addresses:

1.
100 West Washington
Commercial Banking
MAC S4101-251
Phoenix, Arizona 85003
Attention: Keri Tignini
Phone: 602-378-4593
Fax: 602-378-4758