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                                                                 EXHIBIT 4.3.21

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THIS WARRANT AND ANY SECURITIES ACQUIRED UPON THE EXERCISE OF THIS WARRANT HAVE
NOT BEEN REGISTERED UNDER: (A) THE SECURITIES ACT OF 1933, AS AMENDED, IN
RELIANCE UPON THE EXEMPTIONS FROM REGISTRATION PROVIDED IN SECTIONS 3 AND 4 OF
SUCH ACT AND/OR REGULATIONS D PROMULGATED THEREUNDER; OR (B) ANY STATE
SECURITIES LAWS IN RELIANCE UPON APPLICABLE EXEMPTIONS THEREUNDER. THESE
SECURITIES MUST BE ACQUIRED FOR INVESTMENT ONLY FOR THE ACCOUNT OF THE INVESTOR
AND MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SECURITIES LAWS OR AN
OPINION OF COUNSEL ACCEPTABLE TO THE CORPORATION OR ITS REPRESENTATIVES THAT
SUCH SALE OR TRANSFER WOULD NOT VIOLATE APPLICABLE SECURITIES LAWS OR
REGULATIONS.
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WARRANT NO. ____                                              TO PURCHASE______
                                                          SHARES OF COMMON STOCK
                                                              (NO PAR VALUE)

                      CLASS "AG" WARRANT TO PURCHASE SHARES
                               OF COMMON STOCK OF
                                  PROBEX CORP.
                            (A DELAWARE CORPORATION)

                         PURCHASE PRICE PER SHARE: $1.40

EXPIRATION DATE: 5:00 P.M., DALLAS, TEXAS TIME, ON NOVEMBER 30, 2005


         THIS CERTIFIES that, for value received,


is the registered owner and is entitled, subject to the terms and conditions of
this Warrant, until the Expiration Date, to purchase the number of shares set
forth above of the Common Stock, no par value (the "Common Stock"), of Probex
Corp. (the "Corporation") from the Corporation at the purchase price set forth
above. The number of shares of Common Stock which may be received upon the
exercise of the Warrants and the price to be paid for each share of Common Stock
are subject to adjustment from time to time as hereinafter set forth.

1. EXERCISE OF WARRANTS. Subject to the provisions hereof, this Warrant may be
exercised in whole or in part until the Expiration Date, by delivery of this
Warrant to the Corporation with the exercise form duly executed and payment of
the purchase price (in cash or by certified or bank cashier's check made payable
to the order of the Corporation) for each share purchased..

2. CORPORATION'S COVENANTS AS TO COMMON STOCK. Shares deliverable on the
exercise of this Warrant shall, at delivery, be fully paid and non-assessable,
free from taxes, liens, and charges with respect to their purchase. The
Corporation shall at all times reserve and hold available sufficient shares of
Common Stock to satisfy all conversion and purchase rights of outstanding
convertible securities, options and warrants.

3. METHOD OF EXERCISE; FRACTIONAL SHARES. The purchase rights represented by
this Warrant are exercisable at the option of the registered owner in whole at
any time, or in part, from time to time, within the period above specified,
provided, however, that purchase rights are not exercisable with respect to a

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Class "AG" Warrant No. ____
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fraction of a share of Common Stock. In lieu of issuing a fraction of a share
remaining after exercise of this Warrant as to all full shares covered hereby,
the Corporation shall either (1) pay therefor cash equal to the same fraction of
the then current Warrant purchase price per share or, at its option, (2) issue
scrip for the fraction, in registered or bearer form approved by the board of
directors of the Corporation, which shall entitle the holder to receive a
certificate for a full share of Common Stock on surrender of scrip aggregating a
full share. Scrip may become void after a reasonable period (but not less than
six months after the expiration date of this Warrant) determined by the board of
directors and specified in the scrip. In case of the exercise of this Warrant
for less than all the shares purchasable, the Corporation shall cancel the
Warrant and execute and deliver a new Warrant of like tenor and date for the
balance of the shares purchasable.

4. ADJUSTMENT OF SHARES PURCHASABLE. The number of shares purchasable hereunder
and the purchase price per share are subject to adjustment from time to time as
specified in this Warrant.

5. REDEMPTION. The Corporation has no redemption rights pursuant to this
Warrant.

6. LIMITED RIGHTS OF OWNER. This Warrant does not entitle the owner to any
voting rights or other rights as a shareholder of the Corporation, or to any
other rights whatsoever except the rights herein expressed. No dividends are
payable or will accrue on this Warrant or the shares purchasable hereunder
until, and except to the extent that, this Warrant is exercised.

7. EXCHANGE FOR OTHER DENOMINATIONS. This Warrant is exchangeable, on its
surrender by the registered owner to the Corporation, for new Warrants of like
tenor and date representing in the aggregate the right to purchase the number of
shares purchasable hereunder in denominations designated by the registered owner
at the time of surrender.

8. TRANSFER. Except as otherwise above provided, this Warrant is transferable
only on the books of the Corporation by the registered owner in person or by
attorney, on surrender of this Warrant, properly endorsed. However, because this
Warrant has not been registered under the Securities Act of 1933, as amended,
and applicable state securities laws, this Warrant may not be sold or
transferred in the absence of an effective registration of it under such Act and
all other applicable securities laws or an opinion of counsel acceptable to the
Corporation or its representatives that such sale or transfer would not violate
applicable securities laws or regulations. Any Common Stock purchased upon
exercise of this Warrant shall also be subject to the same restrictions on
transfer and will contain the same transfer legend found on the face of this
Warrant.

9, RECOGNITION OF REGISTERED OWNER. Prior to due presentment for registration of
transfer of this Warrant, the Corporation may treat the registered owner as the
person exclusively entitled to receive notices and otherwise to exercise rights
hereunder.

10. EFFECT OF STOCK SPLIT, ETC. If the Corporation, by stock dividend, split,
reverse split, reclassification or shares, or otherwise, changes as a whole the
outstanding Common Stock into a different number or class of shares, then:

         (1) the number and class of shares so changed shall, for the purposes
of this Warrant, replace the shares outstanding immediately prior to the change;
and

         (2) the Warrant purchase price in effect, and the number of shares
purchasable under this Warrant, immediately prior to the date upon which the
change becomes effective, shall be proportionately adjusted (the price to the
nearest cent). Irrespective of any adjustment or change in the Warrant purchase
price or the number of shares purchasable under this or any other Warrant of
like tenor, the Warrants theretofore and thereafter issued may continue to
express the Warrant purchase




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Class "AG" Warrant No. ____
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price per share and the number of shares purchasable as were expressed in the
Warrants when initially issued.

11. EFFECT OF MERGER, ETC. If the Corporation consolidates with or merges into
another corporation, the registered owner shall thereafter be entitled on
exercise to purchase, with respect to each share of Common Stock purchasable
hereunder immediately before the consolidation or merger becomes effective, the
securities or other consideration to which a holder or one share or Common Stock
is entitled in the consolidation or merger to assure that all the provisions or
this Warrant shall thereafter be applicable, as nearly as reasonable may be, to
any securities or other consideration so deliverable on exercise of this
Warrant. The Corporation shall not consolidate or merge unless, prior to
consummation, the successor corporation (if other than the Corporation) assumes
the obligations of this section 11 by written instrument executed and mailed to
the registered owner at the address of the owner on the books of the
Corporation. A sale or lease of all or substantially all the assets of the
Corporation for a consideration (apart from the assumption of obligations)
consisting primarily or securities is a consolidation or merger for the
foregoing purposes.

12. NOTICE OF ADJUSTMENT. On the happening of an event requiring an adjustment
of the Warrant purchase price or shares purchasable hereunder, the Corporation
shall forthwith give written notice to the registered owner stating the adjusted
Warrant purchase price and the adjusted number and kind of securities or other
property purchasable hereunder resulting from the event and setting forth in
reasonable detail the method of calculation and the facts upon which the
calculation is based. The board of directors of the Corporation, acting in good
faith, shall determine the calculation.

13. NOTICE AND EFFECT OF DISSOLUTION, ETC. In case a voluntary or involuntary
dissolution, liquidation, or winding up of the Corporation (other than in
connection with a consolidation or merger covered by Section 11 above) is at any
time proposed, the Corporation shall give at least 10 days' written notice to
the registered owner prior to the record date as of which holders of Common
Stock will be entitled to receive distributions as a result of the proposed
transaction. Such notice shall contain: (1) the date on which the transaction is
to take place; (2) the record date as of which holders of Common Stock will be
entitled to receive distributions as a result of the transaction; (3) a brief
description of the transaction; (4) a brief description of the distributions to
be made to holders of Common Stock as a result of the transaction; and (5)an
estimate of the fair value of the distributions. On the date of the transaction,
if it actually occurs, this Warrant and all rights hereunder shall terminate.

14. METHOD OF GIVING NOTICE; EXTENT REQUIRED. Notices shall be given by first
class mail, postage prepaid, addressed to the registered owner at the address of
the owner appearing in the records of the Corporation. No notice to warrant
holders is required except as specified in Sections 12 and 13.

15. ACCESS TO INFORMATION. The Company will provide an opportunity to any
registered owner of this Warrant to ask questions of management of the Company
and to obtain information to the extent the Company has the same in its
possession prior to any exercise of the owner's rights to purchase Common Stock
under this Warrant. Requests for information and any other questions concerning
the business and affairs of the Company should be directed to any officer of the
Company at its main offices.

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Class "AG" Warrant No. ____
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         Witness the seal of the Corporation and the signatures of its
authorized officers.




Date                      (Seal)             PROBEX CORP.
    ----------------------




ATTEST:



--------------------------------             --------------------------------
Charles M. Rampacek                          Bruce A. Hall
Chief Executive Officer & President          Chief Financial Officer & Secretary


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Class "AG" Warrant No. ____
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                                  TRANSFER FORM



         For value received, the undersigned hereby sells, assigns, and
transfers to

Name
    ----------------------------------

Address
       -------------------------------


this Warrant and irrevocable appoints _________________ attorney (with full
power of substitution) to transfer this Warrant on the books of the Corporation.

Date:



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                                ------------------------------------------------
                                (Please sign exactly as name appears on Warrant)


                                Taxpayer ID No.
                                               ---------------------------------

In the presence of              Signature guaranteed by



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Class "AG" Warrant No. ____
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                                  EXERCISE FORM



         The undersigned hereby: (1) irrevocably subscribes for ________________
shares of your Common Stock pursuant to this Warrant, and encloses payment of
$____________________ therefor; (2) requests that a certificate for the shares
be issued in the name of the undersigned and delivered to the undersigned at the
address below; and (3) if such number of shares is not all of the shares
purchasable hereunder, that a new Warrant of like tenor for the balance of the
remaining shares purchasable hereunder be issued in the name of the undersigned
and delivered to the undersigned at the address below.

Date:



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                                ------------------------------------------------
                                (Please sign exactly as name appears on Warrant)

                                Address:
                                        ----------------------------------------

                                        ----------------------------------------


                                Taxpayer ID No.
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