Document:

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                                                                  EXHIBIT 4.3.22

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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
                                                             ($0.001 PAR VALUE)

                      CLASS "AH" 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 DECEMBER 26, 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, $0.001 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 "AH" Warrant No. ____
Page 2

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 this
Warrant and execute and deliver a new Warrant of like tenor and date for the
balance of the shares purchasable.

4. ADJUSTMENT OF EXERCISE PRICE. If on or prior to January 15, 2003, the
Corporation shall (i) issue, (ii) enter into any binding agreement to issue, or
(iii) commence any public or private offering for the issuance of, shares of
Common Stock, warrants to purchase shares of Common Stock or debt or equity
securities which are convertible into shares of Common Stock, in an aggregate
amount of at least 100,000 shares of Common Stock (excluding any options to
purchase Common Stock issued pursuant to any employee stock option plan of the
Corporation), and the issuance, exercise or conversion price (the "Issuance
Price") of such Common Stock is less than $1.40 per share, then the exercise
price per share pursuant to this Warrant shall be adjusted (and the Corporation
shall, after occurrence of any event requiring such adjustment, notify the
holder of this Warrant of the adjustment) so that the exercise price shall be
equal to the Issuance Price. For purposes of this section, a public or private
offering shall be deemed to have commenced if the there is substantial agreement
as to the material terms of such offering.

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. REGISTRATION RIGHTS.

      (1) Each time that the Corporation proposes for any reason to register any
of its Common Stock under the Securities Act in connection with the proposed
offer and sale of its Common Stock for money either for its own account or on
behalf of any other security holder ("Proposed Registration"), other than
pursuant to a registration statement on Form S-4, S-8 or any successor thereto,
the

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Class "AH" Warrant No. ____
Page 3

Corporation shall promptly give written notice of such Proposed Registration to
the holder hereof and shall offer such holder hereof the right to request
inclusion of the shares issued or issuable upon the exercise of this Warrant in
the Proposed Registration.

      (2) The holder hereof shall have thirty (30) days from the receipt of such
notice to deliver to the Corporation a written request specifying the number of
shares such holder hereof intends to sell and the holder's intended method of
disposition.

      (3) In the event that the Proposed Registration by the Corporation is, in
whole or in part, an underwritten public offering, the Corporation shall so
advise the holder hereof as part of the written notice given pursuant to Section
10(1), and any request under Section 10(2) must specify that the shares of
Common Stock be included in the underwriting on the same terms and conditions as
the shares of Common Stock, if any, otherwise being sold through underwriters
under such registration.

      (4) Upon receipt of a written request pursuant to Section 10(2), the
Corporation shall promptly use its best efforts to cause all such shares of
Common Stock held by the holder hereof to be registered under the Securities Act
(and included in any related qualifications under blue sky laws or other
compliance), to the extent required to permit sale or disposition as set forth
in the Proposed Registration.

      (5) In the event that the offering is to be an underwritten offering, the
holder hereof proposing to distribute its shares of Common Stock through such
underwritten offering agrees to enter into an underwriting agreement with the
underwriter or underwriters selected for such underwriting by the Corporation.

      (6) Notwithstanding the foregoing, if in its good faith judgment, the
managing underwriter determines and advises in writing that the inclusion of all
shares of Common Stock issued or issuable with respect to this Warrant proposed
to be included in the underwritten public offering, together with any other
issued and outstanding shares of Common Stock proposed to be included therein by
holders other than the holder hereof, would interfere with the successful
marketing of such securities, then the number of such shares to be included in
such underwritten public offering shall be reduced, on a pro-rata basis (except
only those shares held by holders that have the benefit of any priority rights
previously granted such holders), based upon the number of shares held by each
holder, including the holder hereof; provided that, in connection with any such
public offering, if the managing underwriter reasonably and in good faith
recommends, which recommendation and supporting reasoning shall be delivered in
writing to the holders, that no amount of shares, including shares held by the
holder hereof, should be included in the underwritten public offering, then the
Corporation shall not be required to include any such shares in such public
offering.

10, 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.

11. EFFECT OF STOCK SPLIT, ETC. If the Corporation, by stock dividend, split,
reverse split, reclassification of 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

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Class "AH" Warrant No. ____
Page 4

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
price per share and the number of shares purchasable as were expressed in the
Warrants when initially issued.

12. 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 of one share of Common Stock
is entitled in the consolidation or merger to assure that all the provisions of
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 13 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 consideration (apart from the assumption of obligations)
consisting primarily of securities is a consolidation or merger for the
foregoing purposes.

13. 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.

14. 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 13 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.

15. 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 5, 10, 14 and 15.

16. ACCESS TO INFORMATION. The Corporation will provide an opportunity to any
registered owner of this Warrant to ask questions of management of the
Corporation and to obtain information to the extent the Corporation has made
such information publicly available 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 Corporation should be
directed to any officer of the Corporation at its main offices.

                  [REMAINDER OF PAGE LEFT BLANK INTENTIONALLY]

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Class "AH" Warrant No. ____
Page 5

      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 "AH" Warrant No. ____
Page 6

                                  TRANSFER FORM

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

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

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

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

Date:

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

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

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

In the presence of              Signature guaranteed by

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

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Class "AH" Warrant No. ____
Page 7

                                  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:

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

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

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

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

                                Taxpayer ID No.
                                               ---------------------------------<PAGE>   1
                                                                   EXHIBIT 10.23

              [CREDIT SUISSE FIRST BOSTON CORPORATION LETTERHEAD]

October 11,2000

Mr. Charles M. Rampacek                           STEVEN S. GREENWALD
Chief Executive Officer & President               Managing Director
Probex Corp.
One Galleria Tower
13355 Noel Road
Suite 1200
Dallas, TX 75240

Dear Charlie:

This letter agreement (the "Engagement") sets forth the terms and conditions
under which Credit Suisse First Boston Corporation and its affiliates,
successors and assigns, as appropriate ("CSFB"), has been engaged to act as
exclusive financial advisor to Probex Corp. ("Probex") in connection with the
structuring and arranging of financing for various lubricating oils reprocessing
projects to be located in the United States and France (the "Project"). The
terms and conditions of this letter agreement are contingent upon CSFB's
completion of due diligence and review and acceptance by its credit and
investment banking committees, currently expected to occur on or prior to
Friday, November 10, 2000.

KEY TASKS

CSFB will, if appropriate and if requested, perform the following key tasks
under this Engagement Letter:

     (a)  assist Probex in the development of a financing plan for the Project
          that will consider (i) bank loans, (ii) equity private placements,
          (iii) capital markets offerings (debt or equity) and (iv) other
          available financing sources (each, a "Financing");

     (b)  assist Probex in its negotiations with parties involved in certain
          agreements relating to the Project such as supply agreements, offtake
          agreements, the EPC contract, etc.;

     (c)  assist Probex in developing a financial model for the Project;

     (d)  assist Probex in the selection of appropriate consultants regarding
          such matters as insurance, market, legal issues and engineering;

     (e)  assist Probex in the preparation and presentation of materials to the
          rating agencies (if applicable) regarding Probex and the Project,
          including leading such rating agencies through on-site due diligence
          of the Project, if necessary or appropriate; and

<PAGE>   2
     (f)  assist Probex in the preparation of descriptive materials, including
          offering documents and term sheets, and any other documents and
          agreements to be used in connection with a Financing of the Project.

INFORMATION

In connection with CSFB's engagement, Probex will furnish CSFB with all
information concerning Probex and the Project which CSFB reasonably requests and
will provide CSFB with access to Probex's officers, directors, employees,
accountants, counsel, and other representatives involved in the Project
(collectively, the "Representatives"), it being understood that CSFB will rely
solely upon such information supplied by Probex and their Representatives
without assuming any responsibility for independent investigation thereof. All
non-public information concerning Probex and the Project which is given to CSFB
in connection with this engagement will be used solely in the course of the
performance of its services hereunder and will be treated confidentially by it
for so long as it remains nonpublic. CSFB will not disclose any such non-public
information to any third party without the consent of Probex, except as
otherwise required by law.

FEES AND EXPENSES

As compensation for CSFB's services hereunder, Probex agrees to pay CSFB the
following fees:

     (a)  a retainer fee equal to (i) US$500,000 earned upon execution of this
          agreement and payable no later than November 30, 2000 (the "Initial
          Retainer Fee"), (ii) $750,000 payable upon the earlier of Probex's
          termination of this agreement and the completion of the first closing
          in connection with a Financing for the Project, and (iii) $750,000
          payable upon the earlier of Probex's termination of this agreement and
          the completion of the second closing in connection with a Financing
          for the Project (collectively, the "Retainer Fee"):

     (b)  in connection with the equity private placement contemplated hereby,
          the Company will pay to CSFB, promptly upon each closing of a sale of
          the Securities, a cash fee equal to 7.00% of the total proceeds raised
          in such sale (the "Placement Fee"); and

     (c)  in connection with bank loans, a net underwriting and arrangement fee
          payable to CSFB equal to the greater of (i) $1,000,000 and (ii) 1.5%
          of the aggregate loan amount, payable upon execution and delivery by
          all parties thereto of definitive credit documentation - exclusive of
          the initial fee paid to banks electing to participate in the Probex
          financing (the "Bank Fee").

NO AGREEMENT TO UNDERWRITE OR PURCHASE FINANCING

CSFB does not hereby undertake to purchase or underwrite any securities or
provide a bank loan in connection with the Project. Any such engagement shall be
subject to a separate agreement (including customary terms, including
indemnification provisions) if CSFB agrees to participate in an underwriting,
debt placement or to provide some portion of a Financing.

<PAGE>   3
EXPENSES

Probex agrees to reimburse CSFB, for its direct and reasonable out-of-pocket
expenses (including, but not limited to, independent engineer or other
consultants, underwriter's counsel, travel and accommodation, telephone,
facsimile, photocopy, but not employee salaries or overhead expenses, provided
that such consultants and counsel are reasonably acceptable to Probex) resulting
from or arising out of this engagement upon receipt of invoice therefor,
quarterly. Any expenses if not previously reimbursed as provided herein, shall
be reimbursed upon the closing of any financing contemplated hereunder or the
date of termination of this agreement, as the case may be.

TERMINATION

CSFB and Probex each may terminate this Engagement Letter with or without cause
at any time upon at least 30 days prior written notice. In the event of a Probex
termination of this agreement for reasons other than a material breach by CSFB
of its obligations hereunder, if within 18 months of such termination Probex
executes a capital markets (debt or equity) or bank financing for the Project,
CSFB shall be entitled to its full Retainer Fee, Placement Fee and Bank Fee as
provided herein. Prior to the first closing in connection with a Financing, in
the event of a CSFB termination of this agreement without cause (unless such
termination is based upon CSFB's view that a Financing in the foreseeable future
cannot be closed), CSFB agrees to reimburse Probex for its payment of the
Initial Retainer Fee (to the extent paid).

No termination hereunder by either CSFB or Probex shall affect Probex's (i)
obligations to pay the Initial Retainer Fee and expenses of CSFB accrued to the
date of termination and (ii) obligations to indemnify CSFB and certain related
entities under the separate letter agreement referred to below. No termination
of CSFB's engagement by Probex shall affect Probex's obligations under the next
paragraph, unless such termination arises out of a willful and material breach
by CSFB of its obligations hereunder.

OTHER MATTERS

For three years following the date of this agreement, Probex agrees to, and
cause its majority owned subsidiaries and the Project to, provide CSFB, and CSFB
agrees to accept, the following assignments:

(a)  CSFB will be sole lead manager or sole placement agent for any capital
     markets or private financing by Probex or its majority owned subsidiaries
     or the Project;

(b)  CSFB will be sole lead manager of equity related transactions for Probex or
     its majority owned subsidiaries or the Project; and

(c)  CSFB will be sole lead arranger and book manager for any bank financing of
     Probex or its majority owned subsidiaries or the Project,

As compensation for any of the foregoing services, CSFB will be paid customary
fees to be mutually agreed upon at the appropriate time. The terms of any such
additional engagements will be set forth in separate letter agreements to be
mutually agreed upon. Probex acknowledges that CSFB's obligation to accept any
such assignment is subject to

<PAGE>   4
(i) approval of our Credit, Equity Valuation and Investment Banking Committees,
as applicable; (ii) satisfactory completion of all regulatory requirements
(including receipt of all necessary approvals) and compliance with all
applicable laws (including, without limitation, those laws governing the sale of
securities); (iii) satisfactory completion of due diligence customary in
transactions of the kind contemplated thereby; (iv) absence of any material
adverse change in the condition (financial and otherwise), business, results of
operations or prospects of Probex or its majority owned subsidiaries or the
Project, as applicable; (v) no adverse change in the business or financial
markets; and (vi) the execution of an underwriting agreement, purchase agreement
or similar transaction document containing customary terms acceptable to CSFB,
including appropriate indemnification provisions. The indemnity agreement
referred to below shall apply to CSFB's activities in connection with any such
additional assignment unless and until superseded by the indemnity provisions
Set forth in any executed agreement relating to such additional assignment and,
subject to the foregoing, shall remain in full force and effect regardless of
any completion, modification or termination of CSFB's engagement.

Since CSFB will be acting on behalf of Probex in connection with the transaction
contemplated herein, Probex has entered into a separate letter agreement with
CSFB, dated the date hereof, providing for the indemnification of CSFB and
certain related persons and entities.

Any amendment to this agreement must be in writing and executed by CSFB and
Probex. This agreement may be signed by CSFB, or Probex in separate counterparts
all of which together shall constitute a single agreement.

Probex agrees that CSFB has the right following the closing of a Financing to
place advertisements in financial and other newspapers and journals at its own
expense describing its services to Probex hereunder, provided that CSFB will
submit a copy of any such advertisements to Probex for its approval, which shall
not be unreasonably withheld.

CSFB agrees that Probex has the right place an announcement in such newspapers
and publications at its own expense, stating that CSFB has been retained as
exclusive financial advisor to Probex, provided that Probex will submit a copy
of any such draft announcement to CSFB for its prior written approval, which
shall not be unreasonably withheld.

In connection with this engagement, CSFB is acting as an independent contractor
with duties owing solely to Probex. This agreement shall be governed by and
construed in accordance with the laws of the State of New York without regard to
conflicts of the law principles thereof,

If CSFB Is given the offer to complete a financing and CSFB declines, Probex is
free to pursue other alternatives without a payment of fees to CSFB.

<PAGE>   5
We look forward to the opportunity to work with you on this assignment. If the
foregoing reflects your understanding, please sign two copies of this letter and
return one copy to CSFB.

Yours sincerely,
CREDIT SUISSE FIRST BOSTON CORPORATION

By:
       ------------------------------------
Name:  Steven S. Greenwald
Title: Managing Director

Agreed and accepted:
PROBEX CORP.

By:     /s/ CHARLES M. RAMPACEK
       ------------------------------------
Name:  Charles M. Rampacek
Title: Chief Executive Officer & President

cc:    Raymond S. Wood
       Kathleen M. Burke
       Lloyd D. Eason
       James S. Finch

<PAGE>   6
TO: Credit Suisse First Boston
    Eleven Madison Avenue                                       OCTOBER 11, 2000
    New York, New York 10010-3629

In further consideration of the agreements contained in our engagement letter
dated the date hereof (the "engagement"), in the event that Credit Suisse First
Boston Corporation ("CSFB") or any of its affiliates, the respective directors,
officers, partners, agents or employees of CSFB or any of its affiliates, or
any other person controlling CSFB or any of its affiliates (collectively,
Indemnified Persons") becomes involved in any capacity in any action, claim,
suit, investigation or proceeding, actual or threatened, brought by or against
any person, including stockholders of PROBEX CORP. (the "Company"), in
connection with or as a result of the engagement or any matter referred to in
the engagement, the Company will reimburse such indemnified Person for its
reasonable and customary legal and other expenses (including without limitation
the costs and expenses incurred in connection with investigating, preparing for
and responding to third party subpoenas or enforcing the engagement) incurred in
connection therewith as such expenses are incurred, except in respect of
expenses that are incurred primarily as a result of Losses that are finally
determined by a court or arbitral tribunal to have resulted from the bad faith
or gross negligence of such Indemnified Person. The Company will also indemnify
and hold harmless any Indemnified Person from and against, and the Company
agrees that no Indemnified Person shall have any liability to the Company or
its owners, parents, affiliates, security holders or creditors for, any losses,
claims, damages or liabilities (including actions or proceedings in respect
thereof) (collectively, "Losses") (A) related to or arising out of (i) the
Company's actions or failures to act (including statements or omissions made or
information provided by the Company or its agents) or (ii) actions or failures
to act by an Indemnified Person with the Company's consent or in reliance on the
Company's actions or failures to act or (B) otherwise related to or arising out
of the engagement or CSFB's performance thereof, except that this clause (B)
shall not apply to any Losses to the extent they are finally determined by a
court or arbitral tribunal to have resulted from the bad faith or gross
negligence of such Indemnified Person. If such indemnification is for any reason
not available or insufficient to hold an Indemnified Person harmless, the
Company agrees to contribute to the Losses involved in such proportion as is
appropriate to reflect the relative benefits received (or anticipated to be
received) by the Company, on the one hand, and by CSFB, on the other hand, with
respect to the engagement or, if such allocation is determined by a court or
arbitral tribunal to be unavailable, in such proportion as is appropriate to
reflect other equitable considerations such as the relative fault of the Company
on the one hand and of CSFB on the other hand; provided, however, that, to the
extent permitted by applicable law, the Indemnified Persons shall not be
responsible for amounts which in the aggregate are in excess of the amount of
all fees actually received by CSFB from the Company in connection with the
engagement. Relative benefits to the Company, on the one hand, and CSFB, on the
other hand, with respect to the engagement shall be deemed to be in the same
proportion as (i) the total value paid or proposed to be paid or received or
proposed to be received by the Company or its security holders, as the case may
be, pursuant to the transaction(s), whether or not consummated, contemplated by
the engagement, bears to (ii) all fees actually received or proposed to be
received by CSFB pursuant to the transaction(s), whether or not consummated, in
connection with the engagement.

The Company will not, without CSFB's prior written consent, settle, compromise,
consent to the entry of any judgment in or otherwise seek to terminate any
action, claim, suit, investigation or proceeding in respect of which
indemnification may be sought hereunder (whether or not any Indemnified Person
is a party thereto) unless the Company exercises

<PAGE>   7
reasonable efforts to assure that such settlement, compromise, consent or
termination includes a release of each Indemnified Person from any liabilities
arising out of such action, claim, suit, investigation or proceeding. The
Company will not permit any such settlement, compromise, consent or termination
to include a statement as to, or an admission of, fault, culpability or a
failure to act by or on behalf of an Indemnified Person, without such
Indemnified Person's prior written consent. No Indemnified Person seeking
indemnification, reimbursement or contribution under this agreement will,
without the Company's prior written consent, settle, compromise, consent to the
entry of any judgment in or otherwise seek to terminate any action, claim, suit,
investigation or proceeding referred to herein.

Prior to entering into any agreement or arrangement with respect to, or
effecting, any merger, statutory exchange or other business combination or
proposed sale or exchange, dividend or other distribution or liquidation of all
or a significant portion of its assets in one or a series of transactions or any
significant recapitalization or reclassification of its outstanding securities
that does not directly or indirectly provide for the assumption of the
obligations of the Company set forth herein. the Company will notify CSFB in
writing thereof (if not previously so notified) and, if requested by CSFB, shall
arrange in connection therewith alternative means of providing for the
obligations 01 the Company set forth herein, including the assumption of such
obligations by another party, insurance, surety bonds or the creation of an
escrow, in each case in an amount and upon terms and conditions satisfactory to
CSFB.

The Company's obligations hereunder shall be in addition to any rights that any
Indemnified Person may have at common law or otherwise, The Company acknowledges
that in connection with the engagement CSFB is acting as an independent
contractor and not in any other capacity with duties owing solely to the
Company. This agreement and any other agreements relating to the engagement
shall be governed by and construed in accordance with the laws of the State of
New York, applicable to contracts made and to be performed therein and, in
connection therewith, the parties hereto consent to the exclusive jurisdiction
of the Supreme Court of the State of New York sitting in New York County or the
United States District Court for the Southern District of New York and the
respective appellate courts thereof. Notwithstanding the foregoing, solely for
purposes of enforcing the Company's obligations hereunder, the Company consents
to personal jurisdiction, service and venue in any court proceeding in which any
claim subject to this agreement is brought by or against any Indemnified Person.
CSFB HEREBY AGREES, AND THE COMPANY HEREBY AGREES ON ITS OWN BEHALF AND, TO THE
EXTENT PERMITTED BY APPLICABLE LAW, ON BEHALF OF ITS SECURITY HOLDERS, TO WAIVE
ANY RIGHT TO TRIAL BY JURY WITH RESPECT TO ANY CLAIM, COUNTERCLAIM OR ACTION
ARISING OUT OF THE ENGAGEMENT OR CSFB'S PERFORMANCE THEREOF.

<PAGE>   8

The provisions of this agreement shall apply to the engagement (including
related activities prior to the date hereof) and any modification thereof and
shall remain in full force and effect regardless of the completion or
termination of the engagement. If any term, provision, covenant or restriction
herein is held by a court of competent jurisdiction to be invalid, void or
unenforceable or against public policy, the remainder of the terms, provisions
and restrictions contained herein shall remain in full force and effect and
shall in no way be affected, impaired or invalidated.

                                    Very truly yours,
                                    PROBEX CORP.

                                    By:    /s/ CHARLES M. RAMPACEK
                                           -----------------------------------
                                    Name:  Charles M. Rampacek
                                    Title: Chief Executive Officer & President

Accepted and agreed to as of the date hereof:
CREDIT SUISSE FIRST BOSTON CORPORATION

By:
       -------------------------------------
Name:  Steven S. Greenwald
Title: Managing Director

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