Document:

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                                                                EXHIBIT 10.21.1

                             SECURED PROMISSORY NOTE

$__________                                                    November 2, 2000

         FOR VALUE RECEIVED, this Secured Promissory Note (this "Note") is made
by Probex Corp., a Delaware corporation ("Maker"), to _________________________
_________________________ ("Payee"). This Note is one of the "Notes" as defined
in, and is entitled to the benefits of, that certain Security Agreement (the
"Security Agreement"), dated as of the date hereof, by and among Maker, Payee,
_____________________________________________________, _______________________
_____________________________________________.

         1. Payments. Maker hereby promises to pay to the order of Payee the
principal sum of ______________________________________ Dollars ($_________) at
_______________, ___________________________, or such other place as the holder
hereof may designate from time to time in writing, in lawful money of the United
States of America and in immediately available funds, together with interest on
the unpaid principal balance hereof at the rate provided herein from the date of
this Note until payment in full of the indebtedness evidenced by this Note. This
Note and all accrued and unpaid interest shall be due and payable in one lump
sum on January 15, 2001. Any payment made under this Note shall be applied first
to interest accrued and unpaid on the outstanding principal balance as of such
date of payment and then to the outstanding principal balance due hereunder. If
any required payment falls due on a Saturday, Sunday or a national or state bank
holiday in Texas, then such date shall be extended to the next succeeding day
that is not a Saturday, Sunday or national or state bank holiday.

         2. Interest Rate. The principal amount outstanding from time to time
hereunder shall bear interest calculated on the basis of a 365-day year, at a
rate equal to twelve percent (12%) per annum.

         3. Voluntary Prepayment. This Note may be prepaid, in whole or in part,
without premium or penalty. All prepayments shall be applied first to accrued
interest and then to principal.

         4. Mandatory Prepayment. Maker shall be required to prepay this Note
upon the cumulative receipt by Maker or its subsidiaries of immediately
available funds equal to or greater than $5,000,000 derived from any type of
equity and/or debt financing benefiting Maker. As long as this Note remains
outstanding, Maker shall accept any reasonable financing proposal when presented
to Maker; provided, however, such proposal's reasonableness is to be determined
by the majority of the voting members of the board of directors of Maker acting
in the exercise of their business judgment.

         5. Event of Default. If any of the following events ("Events of
Default") shall occur:

            (a) Maker shall fail to pay any principal of, or any interest on,
this Note or any other amount payable under this Note, when and as the same
shall become due and payable;

            (b) any representation or warranty made or deemed made by or on
behalf of Maker in the Security Agreement, or any amendment or modification
thereof or waiver thereunder, or in any report, certificate, financial statement
or other document furnished pursuant to or in connection the Security Agreement,
or any amendment or modification thereof or waiver thereunder, shall prove to
have been incorrect when made or deemed made;

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            (c) Maker shall fail to observe or perform any covenant, condition
or agreement contained in the Security Agreement;

            (d) Maker shall fail to make any payment (whether of principal or
interest and regardless of amount) in respect of any indebtedness individually
or in the aggregate in excess of $100,000 ("Material Indebtedness"), when and as
the same shall become due and payable;

            (e) any event or condition occurs that results in any Material
Indebtedness of Maker becoming due prior to its scheduled maturity or that
enables or permits (with or without the giving of notice, the lapse of time or
both) the holder or holders of any Material Indebtedness of Maker or any trustee
or agent on its or their behalf to cause any Material Indebtedness of Maker to
become due, or to require the prepayment, repurchase, redemption or defeasance
thereof, prior to its scheduled maturity;

            (f) an involuntary proceeding shall be commenced or an involuntary
petition shall be filed seeking (i) liquidation, reorganization or other relief
in respect of Maker or its debts, or of a substantial part of its assets, under
any federal, state or foreign bankruptcy, insolvency, receivership or similar
law now or hereafter in effect or (ii) the appointment of a receiver, trustee,
custodian, sequestrator, conservator or similar official for Maker or for a
substantial part of its assets, and, in any such case, such proceeding or
petition shall continue undismissed for 60 days or an order or decree approving
or ordering any of the foregoing shall be entered;

            (g) Maker shall (i) voluntarily commence any proceeding or file any
petition seeking liquidation, reorganization or other relief under any federal,
state or foreign bankruptcy, insolvency, receivership or similar law now or
hereafter in effect, (ii) consent to the institution of, or fail to contest in a
timely and appropriate manner, any proceeding or petition described in clause
(f) of this Section, (iii) apply for or consent to the appointment of a
receiver, trustee, custodian, sequestrator, conservator or similar official for
Maker or for a substantial part of its assets, (iv) file an answer admitting the
material allegations of a petition filed against it in any such proceeding, (v)
make a general assignment for the benefit of creditors or (vi) take any action
for the purpose of effecting any of the foregoing;

            (h) Maker shall become unable, admit in writing its inability or
fail generally to pay its debts as they become due;

            (i) one or more judgments for the payment of money in an aggregate
amount in excess of $100,000 shall be rendered against Maker and the same shall
remain undischarged for a period of thirty (30) days during which execution
shall not be effectively stayed, or any action shall be legally taken by a
judgment creditor to attach or levy upon any assets of Maker to enforce any such
judgment;

            (j) any lien purported to be created under the Security Agreement
shall cease to be, or shall be asserted by Maker or any affiliate thereof not to
be, a valid and perfected lien on the Collateral (as defined in the Security
Agreement), with the priority required by the Security Agreement, except (i) as
a result of the sale or other disposition of the Collateral in a transaction
permitted under the Security Agreement or (ii) as a result of Payee's failure to
maintain possession of any promissory notes or other instruments delivered to it
under the applicable Security Agreement;

            (k) there shall occur, in the judgment of Payee, a material adverse
change in the business, assets or prospects of Maker after the date hereof;

            (l) there shall occur any material loss, theft, damage or
destruction of any of Maker's property or assets not fully covered by insurance;
or

            (m) there shall occur a cessation of a substantial part of the
business of Maker for a period which significantly effects its respective
capacity to continue its business on a profitable basis; or Maker shall suffer
the loss or revocation of any license or permit now held or hereafter acquired
by it which is necessary to the continued or lawful operation of its respective
business; or Maker shall be enjoined, restrained or in any way prevented by
court, governmental or administration order from

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conducting all or any material part of its respective business affairs; or any
material part of Maker's property shall be taken through condemnation or the
value of such property shall be materially impaired through condemnation;

then, and in every such event (other than an event described in clause (f) or
(g) of this Section), and at any time thereafter during the continuance of such
event, the Payee may declare the then outstanding amounts hereunder to be due
and payable in whole (or in part, in which case any principal not so declared to
be due and payable may thereafter be declared to be due and payable), and
thereupon the principal of the amounts hereunder so declared to be due and
payable, together with accrued interest thereon and all other obligations of
Maker accrued hereunder, shall become due and payable immediately, without
presentment, demand, protest or other notice of any kind, all of which are
hereby waived by Maker; and in case of any event with respect to Maker described
in clause (f) or (g) of this Section, the principal amounts hereunder then
outstanding, together with accrued interest thereon and all other obligations of
Maker accrued hereunder, shall automatically become due and payable, without
presentment, demand, protest or other notice of any kind, all of which are
hereby waived by Maker.

         6. Remedies Cumulative. The remedies of Payee, as provided herein,
shall be cumulative and concurrent, and may be pursued singularly, successively
or together, at the sole discretion of Payee, and may be exercised as often as
occasion therefor shall arise. No act of omission or commission of Payee,
including specifically any failure to exercise any right, remedy or recourse,
shall be deemed to be a waiver or release of the same, such waiver or release to
be effected only through a written document executed by Payee and then only to
the extent specifically recited therein. A waiver or release with reference to
any one event shall not be construed as continuing, as a bar to, or as a waiver
or release of, any subsequent right, remedy or recourse as to a subsequent
event.

         7. Notices. Except as otherwise provided herein, any notice or demand
which, by the provisions hereof, is required or which may be given to or served
upon Maker or Payee shall be in writing and, if by telecopy, shall be deemed to
have been validly served, given or delivered when transmitted with a copy
immediately mailed by registered or certified mail, if by personal delivery,
shall be deemed to have been validly served, given or delivered upon actual
delivery and, if mailed, shall be deemed to have been validly served, given or
delivered three (3) business days after deposit in the United States mails, as
registered or certified mail, with proper postage prepaid and addressed to the
party to be notified, at the addresses last given in writing by Maker and Payee.

         8. Successors and Assigns. This Note shall be binding upon Maker and
its successors and assigns (including, without limitation, a receiver, trustee
or debtor-in-possession of or for Maker) and shall inure to the benefit of Payee
and its successors and assigns. Maker may not assign its rights hereunder
without the prior written consent of Payee, in its sole discretion, other than
by operation of law. Payee may assign all or a part of its interest in this Note
or its rights hereunder to any party without the prior written consent of Maker,
in its sole discretion, other than by operation of law.

         9. GOVERNING LAW. THIS NOTE SHALL BE DEEMED A CONTRACT AND INSTRUMENT
MADE UNDER THE LAWS OF THE STATE OF TEXAS AND ACCEPTED BY PAYEE IN SAID STATE,
AND ANY AND ALL CLAIMS, DEMANDS OR ACTIONS IN ANY WAY RELATING THERETO OR
INVOLVING ANY DISPUTE BETWEEN ANY OF THE PARTIES TO THIS NOTE, WHETHER ARISING
IN CONTRACT OR TORT, AT LAW, IN EQUITY OR STATUTORILY, SHALL BE CONSTRUED AND
ENFORCED IN ACCORDANCE WITH AND/OR GOVERNED BY THE LAWS OF THE STATE OF TEXAS
(EXCEPTING ITS CHOICE OF LAW RULES) AND THE LAWS OF THE UNITED STATES OF
AMERICA.

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         10. Severability. If any provisions of this Note or any payments
pursuant to the terms hereof shall be invalid or unenforceable to any extent,
the remainder of this Note and any other payments hereunder shall not be
affected thereby and shall be enforceable to the greatest extent permitted by
law. Furthermore, in lieu of such invalid or unenforceable provisions, there
shall be added automatically as part of this Note, a provision or provisions as
similar in its or their terms to such invalid or unenforceable provisions as may
be possible and be legal, valid and enforceable.

         11. No Oral Agreements. This Note and the Security Agreement as written
represent the final agreement between Maker and Payee with respect to the
matters contained therein and may not be contradicted by evidence of prior,
contemporaneous or subsequent oral agreements between Maker and Payee. There are
no unwritten agreements between Maker and Payee.

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         IN WITNESS WHEREOF, Maker has executed and delivered this Note as of
the date and year first above written.

                                            MAKER:

                                            PROBEX CORP.,
                                            a Delaware corporation

                                            By:
                                                -------------------------------
                                            Name:
                                                 ------------------------------
                                            Title:
                                                   ----------------------------

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                                                                 EXHIBIT 10.21.2

                               SECURITY AGREEMENT

         THIS SECURITY AGREEMENT ("Agreement"), dated as of November 2, 2000, is
by and among Probex Corp., a Delaware corporation ("Debtor"), Cambridge
Strategies Group, LLC, a Texas limited liability company ("Collateral Agent"),
Michael and Cindi Crockett, each individual residents of the State of Illinois,
and Beachcraft Limited Partnership, a Texas limited partnership (together with
Collateral Agent, collectively, "Secured Parties").

                                    RECITALS:

         A. Concurrently with the execution of this Agreement, Debtor is
executing those certain Secured Promissory Notes in the original aggregate
principal amount of $1,250,000, in favor of Secured Parties (as amended,
restated or modified, the "Notes").

         B. The execution and delivery of this Agreement is required by the
terms of the Notes and is a condition to their effectiveness.

         NOW THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

                          Security Interest and Pledge

         Section 1. Security Interest and Pledge. As collateral security for the
prompt payment in full when due of all of the obligations, indebtedness and
liabilities of Debtor to Secured Parties arising pursuant to or in connection
with the Notes or this Agreement, whether now existing or hereafter arising,
whether direct, indirect, fixed, contingent, liquidated, unliquidated, joint,
several, or joint and several, Debtor hereby pledges and grants to Secured
Parties, a security interest in and to all of Debtor's right, title and interest
in and to the following (such property being hereinafter sometimes called the
"Collateral"):

         (a) all accounts, accounts receivable, documents, instruments, chattel
     paper, and general intangibles of Debtor and all products and proceeds
     thereof; and

         (b) all equipment, inventory, machinery, and fixtures of Debtor and all
     accessions thereto and all products and proceeds thereof;

provided, however, the Collateral shall exclude (i) all Intellectual Property of
Debtor and its subsidiaries (for purposes of this Agreement, "Intellectual
Property" means, with respect to any entity, proprietary information, trade
secret or knowledge, including, without limitation, confidential information,
patents, trademarks, service marks, inventions, products, designs, development
techniques, methods, know-how, techniques, systems, processes, software
programs, works of authorship, formulae and any other information of a technical
nature), and (ii) all accounts, accounts receivable, documents, instruments,
chattel paper, general intangibles, equipment, inventory, machinery, and
fixtures and all accessions thereto and all products and proceeds thereof of
Debtor's subsidiary, Probex Fluids Recovery, Inc. ("PFR")

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and all capital stock of PFR (collectively, the "PFR Assets"), all of which are
subject to a lien and security interest in favor of Pennzoil-Quaker State
Company.

         Section 1. 2 Obligations. The Collateral shall secure the following
obligations, indebtedness and liabilities of Debtor (all such obligations and
indebtedness being hereinafter sometimes called the "Obligations"):

         (a) the obligations and indebtedness of Debtor to Secured Parties
     evidenced by the Notes;

         (b) all costs and expenses, including, without limitation, all
     attorneys' fees and legal expenses, incurred by Collateral Agent to
     preserve and maintain the Collateral, collect the obligations herein
     described, and enforce this Agreement;

         (c) all extensions, renewals and modifications of any of the foregoing.

                         Representations and Warranties

         To induce Secured Parties to enter into this Agreement, Debtor
represents and warrants to Secured Parties that:

         Section 2.1 Title. Except for the security interest granted herein,
Debtor owns, and with respect to the Collateral acquired after the date hereof
Debtor will own, the Collateral free and clear of any lien, security interest,
or other encumbrance.

         Section 2.2 Accounts. Unless Debtor has given Collateral Agent written
notice to the contrary, whenever the security interest granted hereunder
attaches to an account, Debtor shall be deemed to have represented and warranted
to Secured Parties as to each and all of its accounts that (i) each account is
genuine and in all respects what it purports to be, (ii) each account represents
the legal, valid, and binding obligation of the account debtor evidencing
indebtedness unpaid and owed by such account debtor arising out of the
performance of labor or services by Debtor or the sale or lease of goods by
Debtor, (iii) the amount of each account represented as owing is the correct
amount actually and unconditionally owing except for normal trade discounts
granted in the ordinary course of business, and (iv) no account is subject to
any offset, counterclaim, or other defense.

         Section 2.3 Financing Statements. No financing statement, security
agreement, or other lien instrument covering all or any part of the Collateral
is on file in any public office, except as may have been filed in favor of
Collateral Agent pursuant to this Agreement.

         Section 2.4 Organization and Authority. Debtor is a corporation duly
organized, validly existing, and in good standing under the laws of its state of
incorporation. Debtor has the corporate power and authority to execute, deliver,
and perform this Agreement, and the execution, delivery, and performance of this
Agreement by Debtor has been authorized by all necessary corporate action on the
part of Debtor and does not and will not violate any law, rule or regulation or
the articles of incorporation or bylaws of Debtor and does not and will not
conflict with, result in a breach of, or constitute a default under the
provisions of any indenture, mortgage, deed of trust, security agreement, or
other instrument or agreement pursuant to which Debtor or any of its property is
bound.

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         Section 2.5 Principal Place of Business. The principal place of
business and chief executive office of Debtor, and the office where Debtor keeps
its books and records, is located at the address of Debtor shown beside its name
on the signature page hereof.

         Section 2.6 Location of Collateral. All inventory, machinery, and
equipment of Debtor are located in Dallas County or Denton County, Texas.

                       Affirmative and Negative Covenants

         Debtor covenants and agrees with Secured Parties that:

         Section 3.1 Maintenance. Debtor shall maintain the Collateral in good
operating condition and repair and shall not permit any waste or destruction of
the Collateral or any part thereof. Debtor shall not use or permit the
Collateral to be used in violation of any law or inconsistently with the terms
of any policy of insurance. Debtor shall not use or permit the Collateral to be
used in any manner or for any purpose that would impair the value of the
Collateral or expose the Collateral to unusual risk.

         Section 3.2 Encumbrances. Debtor shall not create, permit, or suffer to
exist, and shall defend the Collateral against, any lien, security interest, or
other encumbrance on the Collateral except the pledge and security interest of
Secured Parties hereunder, and shall defend Debtor's rights in the Collateral
and Secured Parties' security interest in the Collateral against the claims of
all others.

         Section 3.3 Modification of Collateral. Debtor shall do nothing to
impair the rights of Secured Parties in the Collateral. Without the prior
written consent of Collateral Agent, Debtor shall not grant any extension of
time for any payment with respect to the Collateral, or compromise, compound, or
settle any of the Collateral, or release in whole or in part any person or
entity liable for payment with respect to the Collateral, or allow any credit or
discount for payment with respect to the Collateral other than normal trade
discounts granted in the ordinary course of business, or release any lien,
security interest, or assignment securing the Collateral, or otherwise amend or
modify any of the Collateral.

         Section 3.4 Sale of Collateral. Debtor shall not sell, assign, or
otherwise dispose of the Collateral or any part thereof without the prior
written consent of Collateral Agent.

         Section 3.5 Further Assurances. At any time and from time to time, upon
the request of Collateral Agent, and at the sole expense of Debtor, Debtor shall
promptly execute and deliver all such further instruments and documents and take
such further action as Secured Parties may deem necessary or desirable to
preserve and perfect their security interest in the Collateral and carry out the
provisions and purposes of this Agreement, including, without limitation, the
execution and filing of such financing statements as Collateral Agent may
require. A carbon, photographic, or other reproduction of this Agreement or of
any financing statement covering the Collateral or any part thereof shall be
sufficient as a financing statement and may be filed as a financing statement.

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         Section 3.6 Risk of Loss; Insurance. Debtor shall be responsible for
any loss of or damage to the Collateral. Debtor shall maintain, with financially
sound and reputable companies, insurance policies (i) insuring the Collateral
against loss by fire, explosion, theft, and such other risks and casualties as
are customarily insured against by companies engaged in the same or a similar
business, and (ii) insuring Debtor and Secured Parties against liability for
personal injury and property damage relating to the Collateral, such policies to
be in such amounts and covering such risks as are customarily insured against by
companies engaged in the same or a similar business, with losses payable to
Debtor and Secured Parties as their respective interests may appear. All
insurance with respect to the Collateral shall provide that no cancellation,
reduction in amount, or change in coverage thereof shall be effective unless
Collateral Agent has received thirty (30) days prior written notice thereof.
Debtor shall deliver to Collateral Agent copies of all insurance policies
covering the Collateral or any part thereof.

         Section 3.7 Warehouse Receipts Non-Negotiable. Debtor agrees that if
any warehouse receipt or receipt in the nature of a warehouse receipt is issued
with respect to any of its inventory, such warehouse receipt or receipt in the
nature thereof shall not be "negotiable" (as such term is used in Section 7-104
of the Uniform Commercial Code as adopted by the State of Texas).

         Section 3.8 Inspection Rights. Debtor shall permit Collateral Agent and
its representatives to examine or inspect the Collateral wherever located and to
examine, inspect, and copy Debtor's books and records at any reasonable time and
as often as Collateral Agent may desire.

         Section 3.9 Taxes. Debtor agrees to pay or discharge prior to
delinquency all taxes, assessments, levies, and other governmental charges
imposed on it or its property, except Debtor shall not be required to pay or
discharge any tax, assessment, levy, or other governmental charge if (i) the
amount or validity thereof is being contested by Debtor in good faith by
appropriate proceedings diligently pursued, (ii) such proceedings do not involve
any risk of sale, forfeiture, or loss of the Collateral or any interest therein,
and (iii) adequate reserves therefor have been established in conformity with
generally accepted accounting principles.

         Section 3.10 Obligations. Debtor shall duly and punctually pay and
perform the Obligations.

         Section 3.11 Notification. Debtor shall promptly notify Collateral
Agent of (i) any lien, security interest, encumbrance, or claim made or
threatened against the Collateral, (ii) any material change in the Collateral,
including, without limitation, any material damage to or loss of the Collateral,
and (iii) the occurrence or existence of any Event of Default (as defined in the
Notes) or the occurrence or existence of any condition or event that, with the
giving of notice or lapse of time or both, would be an Event of Default.

         Section 3.12 Corporate Changes. Debtor shall not change its name,
identity, or corporate structure in any manner that might make any financing
statement filed in connection with this Agreement seriously misleading unless
Debtor shall have given Collateral Agent thirty (30) days prior written notice
thereof and shall have taken all action deemed necessary or desirable by
Collateral Agent to make each financing statement not seriously misleading.
Debtor shall not change its principal place of business, chief executive office,
or the place where it keeps its books and

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records unless it shall have given Collateral Agent thirty (30) days prior
written notice thereof and shall have taken all action deemed necessary or
desirable by Collateral Agent to cause the security interest in the Collateral
to be perfected with the priority required by this Agreement.

         Section 3.13 Books and Records; Information. Debtor shall keep accurate
and complete books and records of the Collateral and Debtor's business and
financial condition in accordance with generally accepted accounting principles
consistently applied. Debtor shall from time to time at the request of
Collateral Agent deliver to Collateral Agent such information regarding the
Collateral and Debtor as Collateral Agent may request, including, without
limitation, lists and descriptions of the Collateral and evidence of the
identity and existence of the Collateral. Debtor shall mark its books and
records to reflect the security interest of Secured Parties under this
Agreement.

         Section 3.14 Compliance with Agreements. Debtor shall comply in all
material respects with all mortgages, deeds of trust, instruments, and other
agreements binding on it or affecting its properties or business.

         Section 3.15 Compliance with Laws. Debtor shall comply with all
applicable laws, rules, regulations, and orders of any court or governmental
authority.

         Section 3.16 Location of Collateral. Debtor shall not move any of its
equipment, machinery, or inventory from the locations specified herein without
the prior written consent of Collateral Agent.

         Section 3.17 Intellectual Property. So long as any of the Obligations
remain outstanding, Debtor shall not create, permit, or suffer to exist, any
lien, security interest, or other encumbrance on, and shall not sell, assign, or
otherwise dispose of, the Intellectual Property, in any case without the prior
written consent of Collateral Agent.

                      Rights of Secured Parties and Debtor

         Section 4.1 Power of Attorney. DEBTOR HEREBY IRREVOCABLY CONSTITUTES
AND APPOINTS COLLATERAL AGENT AND ANY OFFICER OR AGENT THEREOF, WITH FULL POWER
OF SUBSTITUTION, AS ITS TRUE AND LAWFUL ATTORNEY-IN-FACT WITH FULL IRREVOCABLE
POWER AND AUTHORITY IN THE PLACE AND STEAD AND IN THE NAME OF DEBTOR OR IN ITS
OWN NAME, FROM TIME TO TIME IN COLLATERAL AGENT'S DISCRETION, TO TAKE ANY AND
ALL ACTION AND TO EXECUTE ANY AND ALL DOCUMENTS AND INSTRUMENTS WHICH MAY BE
NECESSARY OR DESIRABLE TO ACCOMPLISH THE PURPOSES OF THIS AGREEMENT. THIS POWER
OF ATTORNEY IS A POWER COUPLED WITH AN INTEREST AND SHALL BE IRREVOCABLE.
Collateral Agent shall not be under any duty to exercise or withhold the
exercise of any of the rights, powers, privileges, and options expressly or
implicitly granted to Secured Parties in this Agreement, and shall not be liable
for any failure to do so or any delay in doing so. Collateral Agent shall not be
liable for any act or omission or for any error of judgment or any mistake of
fact or law in its individual capacity or in its capacity as attorney-in-fact
except acts or omissions resulting from its willful misconduct. This power of
attorney is conferred on Collateral Agent solely to protect, preserve, and
realize upon Secured Parties' security interest in the Collateral.

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         Section 4.2 Secured Parties' Duty of Care. Other than the exercise of
reasonable care in the physical custody of the Collateral while held by Secured
Parties hereunder, Secured Parties shall not have any responsibility for or
obligation or duty with respect to all or any part of the Collateral or any
matter or proceeding arising out of or relating thereto, including, without
limitation, any obligation or duty to collect any sums due in respect thereof or
to protect or preserve any rights against prior parties or any other rights
pertaining thereto, it being understood and agreed that Debtor shall be
responsible for preservation of all rights in the Collateral. Without limiting
the generality of the foregoing, Secured Parties shall be conclusively deemed to
have exercised reasonable care in the custody of the Collateral if Secured
Parties take such action, for purposes of preserving rights in the Collateral,
as Debtor may reasonably request in writing, but no failure or omission or delay
by Secured Parties in complying with any such request by Debtor, and no refusal
by Secured Parties to comply with any such request by Debtor, shall be deemed to
be a failure to exercise reasonable care.

                                     Default

         Section 5. Rights and Remedies. If any event of default shall occur
under either the Notes or this Agreement, Secured Parties shall have all of the
rights and remedies of secured parties under the Uniform Commercial Code as
adopted by the State of Texas as well as any other rights and remedies permitted
under or provided by applicable law.

                         Agreement Among Secured Parties

         Section 6.1 Financing Statement. Secured Parties together will file one
financing statement covering all of the Collateral in the name of the Collateral
Agent in order to simultaneously perfect their security interest in the
Collateral.

         Section 6.2 Appointment of Collateral Agent. Collateral Agent is hereby
appointed, empowered and authorized to act as the agent-in-fact for each Secured
Party for the sole purpose of filing the financing statements and enforcing
Secured Parties' rights under their respective Notes and this Agreement. Each
Secured Party hereby appoints and authorizes Collateral Agent to take such
action as agent on its behalf and to exercise such powers under this Agreement
as are delegated to Collateral Agent by the terms hereof, together with such
powers as are reasonably incidental thereto. As to any matters not expressly
provided for by this Agreement and the Notes, Collateral Agent may, but shall
not be required to, exercise discretion or to take any action that it deems
reasonable, but shall be required to act or to refrain from acting upon the
written instructions of all of Secured Parties; provided, however, that
Collateral Agent shall not be required to take any action that is contrary to
this Agreement, the Notes or applicable law.

         Section 6.3 Duties. Collateral Agent shall have the exclusive authority
to seek administration, enforcement and collection of the Debtor's obligations
under each of the Notes and this Agreement. Absent the unwillingness of
Collateral Agent to enforce Secured Parties' rights under this Agreement,
Secured Parties shall refrain from independently seeking collection and
enforcement of the obligations under this Agreement. If one of Secured Parties
shall obtain any

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payment or funds, except as otherwise expressly provided for herein (whether
voluntary, involuntary, through the exercise of any right of set-off or
otherwise), in excess of its pro rata share of payments, such recipient Secured
Party shall pay to the Collateral Agent its pro rata share of such excess
payment or funds, and Collateral Agent shall reallocate such funds pro rata
among all of Secured Parties. If all or a portion of any payment received by one
of Secured Parties is held to constitute a preference or otherwise recovered
under the bankruptcy laws, or if for any other reason such Secured Party is
required to refund such payment or pay the amount thereof to Debtor or any third
party, the Collateral Agent shall pay such Secured Party its pro rata share of
such recovered payment.

         Section 6.4 Enforcement. Upon enforcement and collection of the
obligations in whole or in part under this Agreement, Secured Parties will share
pro rata in the proceeds resulting from such collections based upon the ratio of
the amount due and owing to Secured Parties under their respective Notes to the
aggregate amount due and owing under all of the Notes.

                                  Miscellaneous

         Section 7.1 No Waiver; Cumulative Remedies. No failure on the part of
Secured Parties to exercise and no delay in exercising, and no course of dealing
with respect to, any right, power, or privilege under this Agreement shall
operate as a waiver thereof, nor shall any single or partial exercise of any
right, power, or privilege under this Agreement preclude any other or further
exercise thereof or the exercise of any other right, power, or privilege. The
rights and remedies provided for in this Agreement are cumulative and not
exclusive of any rights and remedies provided by law.

         Section 7.2 Successors and Assigns. This Agreement shall be binding
upon and inure to the benefit of Debtor and Secured Parties and their respective
heirs, personal representatives, successors and assigns, except that Debtor may
not assign any of its rights or obligations under this Agreement without the
prior written consent of Secured Parties.

         Section 7.3 Amendment; Entire Agreement. THIS AGREEMENT EMBODIES THE
FINAL, ENTIRE AGREEMENT AMONG THE PARTIES HERETO AND SUPERSEDES ANY AND ALL
PRIOR COMMITMENTS, AGREEMENTS, REPRESENTATIONS, AND UNDERSTANDINGS, WHETHER
WRITTEN OR ORAL, RELATING TO THE SUBJECT MATTER HEREOF AND MAY NOT BE
CONTRADICTED OR VARIED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL
AGREEMENTS OR DISCUSSIONS OF THE PARTIES HERETO. THERE ARE NO ORAL AGREEMENTS
AMONG THE PARTIES HERETO. The provisions of this Agreement may be amended or
waived only by an instrument in writing signed by the parties hereto.

         Section 7.4 Notices. All notices and other communications provided for
in this Agreement shall be given or made in writing and telecopied, mailed by
certified mail return receipt requested, or delivered to the intended recipient
at the "Address for Notices" specified beside its name on the signature pages
hereof; or, as to any party at such other address as shall be designated by such
party in a notice to the other party given in accordance with this Section.
Except as otherwise provided in this Agreement, all such communications shall be
deemed to have been duly given when transmitted by telecopy, subject to
telephone confirmation of receipt, or when personally delivered

                                       7
<PAGE>   8

or, in the case of a mailed notice, three (3) days business days after deposit
in the mails, in each case given or addressed as aforesaid.

         Section 7.5 Applicable Law; Venue; Service of Process. This Agreement
shall be governed by and construed in accordance with the laws of the State of
TEXAS and the applicable laws of the United States of America.

         Section 7.6 Counterparts. This Agreement may be executed in any number
of counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same agreement.

         Section 7.7 Severability. Any provision of this Agreement which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions of this Agreement, and any such
prohibition or unenforceability in any jurisdiction shall not invalidate or
render unenforceable such provision in any other jurisdiction.

         Section 7.8 Headings. The headings, captions and arrangements used in
this Agreement are for convenience only and shall not affect the interpretation
of this Agreement.

         Section 7.9 Construction. Debtor and Secured Parties acknowledge that
each of them has had the benefit of legal counsel of its own choice and has been
afforded an opportunity to review this Agreement with its legal counsel and that
this Agreement shall be construed as if jointly drafted by Debtor and Secured
Parties.

                  [REMAINDER OF PAGE LEFT BLANK INTENTIONALLY]

<PAGE>   9

         IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the day and year first written above.

                                            DEBTOR:

                                            PROBEX CORP.,
                                            a Delaware corporation
Address:
13355 Noel Road, Suite 1200                 By:   /s/ M. R. MACDONALD
Dallas, Texas 75240                             -------------------------------
Attn:  Bruce A. Hall, CFO                   Name:     M. R. MacDonald
Facsimile:  (972) 980-8545                       ------------------------------
                                            Title:    Senior Vice President
                                                   ----------------------------

                                            SECURED PARTIES:

                                            CAMBRIDGE STRATEGIES GROUP, LLC
Address:

P.O. Box 117661                             By:   /s/ RONALD JAMES TISO
Carrollton, TX 75011-7661                       -------------------------------
Attn: Ronald Tiso                           Name:     Ronald James Tiso
Facsimile: (972) 492-4092                        ------------------------------
                                            Title:    Managing Partner
                                                   ----------------------------

Address:                                    -----------------------------------
                                            Michael Crockett
5517 N. Kildare Ave.
Chicago, IL 60630
Attn: Michael Crockett                      -----------------------------------
Facsimile:______________                    Cindi Crockett

                                            BEACHCRAFT LIMITED PARTNERSHIP
Address:

P.O. Box 280                                By:  /s/ JIM McCOURT
Cookville, TX 75558                             -------------------------------
Attn: ___________________                   Name:    By Jim McCourt as
                                                     General Partner
Facsimile: ______________                        ------------------------------
                                            Title:   for Beachcraft Partnership
                                                     Trust
                                                     for Beachcraft Limited
                                                     Partnership
                                                   ----------------------------

                                       9

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