EXHIBIT 10.29.3

                      INTERCREDITOR AND SECURITY AGREEMENT

         THIS  INTERCREDITOR AND SECURITY AGREEMENT  ("Agreement"),  dated as of
September  7,  2001,  is by and  among  Probex  Corp.,  a  Delaware  corporation
("Debtor"),  United  Infrastructure  Company,  LLC, a Delaware limited liability
company (the  "Collateral  Agent"),  and the parties  listed on Exhibit A hereto
(each a "Secured Party", and, collectively, the "Secured Parties").

                                    RECITALS:

         WHEREAS,  as of the date hereof,  Debtor is executing and delivering to
the Secured  Parties  those  certain  Secured  Promissory  Notes in the original
aggregate  principal  amount of $3,000,000,  in favor of the Secured Parties (as
amended, restated or modified, the "Notes").


         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 1.1 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 the  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 ("Obligations"),  Debtor hereby pledges and
grants to the  Collateral  Agent,  as agent  for the  Secured  Parties,  a third
priority security  interest in and to all of Debtor's right,  title and interest
in and to the following  property now owned or hereafter acquired (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 capital stock of Probex Fluids Recovery,  Inc., a Delaware
corporation and the wholly-owned subsidiary of Debtor ("PFR"), evidenced by that
certain  Pledge  Agreement,  dated as of November 29,  2000,  by and between the
Debtor and Wilmington Trust Company ("WTC"), as collateral agent for the secured
parties named therein, and acknowledged by PFR.

         Section 1. 2 Obligations.  The Collateral shall secure the Obligations,
including, without limitation:

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

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

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

                         Representations and Warranties

         To induce the Secured Parties to enter into this Agreement and purchase
the Notes, except as disclosed in the disclosure schedule to this Agreement (the
"Disclosure  Schedule"),  attached  hereto as  Exhibit B,  which  qualifies  the
following  representations  and warranties to the extent apparent on the face of
such disclosures, Debtor represents and warrants to the Secured Parties that:

         Section 2.1 Title.  Except for the first and second  priority  security
interests  granted  to the  secured  parties  named  in those  certain  Security
Agreements dated February 20, 2001 and July 13, 2001,  respectively  (the "Prior
Secured  Parties"),  and 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.  As to all accounts  existing on the date hereof
and whenever the security  interest  granted  hereunder  attaches to an account,
Debtor shall be deemed to have  represented and warranted to the 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 the
collateral  agents  for the Prior  Secured  Parties,  and the  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 the State of
Delaware.  Debtor has the corporate power and authority to execute, deliver, and
perform this  Agreement,  the Notes,  the Loan  Agreement  and the  Registration
Rights  Agreement,  and  the  execution,   delivery,  and  performance  of  this
Agreement,  the Notes, the Loan Agreement and the Registration  Rights Agreement
by Debtor has been authorized by all necessary  corporate  action on the part of
Debtor.

         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.

         Section  2.7  Capitalization.  As of the date  hereof,  the  authorized
capital stock of Debtor consists of:

                  (a) One Hundred Million  (100,000,000) shares of common stock,
$0.001 par value per share (the "Common Stock"), of which 29,411,404 shares were
outstanding,  all of which are duly authorized,  validly issued,  fully-paid and
non-assessable.

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                  (b) Ten Million (10,000,000) shares of preferred stock, $0.001
par value  per share  (the  "Preferred  Stock"),  of which  five  hundred  fifty
thousand  (550,000)  shares  have been  designated  as  Series A 10%  Cumulative
Convertible  Preferred  Stock, and 532,500 of which are outstanding and are duly
authorized, validly issued, fully-paid and non-assessable.

                  (c) Schedule 2.7(c) of the Disclosure  Schedule  discloses all
outstanding options or warrants for the purchase of, or other rights to purchase
or  subscribe  for,  or  securities  convertible  into or  exchangeable  for, or
otherwise  entitling the holder to acquire,  Common Stock or other capital stock
of Debtor,  or any  contracts  or  commitments  to issue or sell Common Stock or
other  capital stock of Debtor or any such  options,  warrants,  rights or other
securities.

                  (d) Debtor has duly reserved from its  authorized and unissued
shares of Common  Stock the full number of shares  required for (a) all options,
warrants,  convertible securities,  exchangeable securities, and other rights to
acquire  shares of Common  Stock  which are  outstanding,  and (b) all shares of
Common  Stock and options  and other  rights to acquire  shares of Common  Stock
which may be issued or granted  under the stock  option and similar  plans which
have been adopted by Debtor or any of its  subsidiaries.  Each outstanding class
or series of securities for which any  anti-dilution  adjustment will occur as a
result of the issuance and sale of the Notes, the conversion of the Notes or the
issuance  of shares of Common  Stock upon any  extension  of the  Maturity  Date
thereof is identified on Schedule  2.7(d) of the  Disclosure  Schedule  attached
hereto, together with the amount of such anti-dilution  adjustment for each such
class or series. The outstanding shares of Common Stock and outstanding options,
warrants  and other  securities  entitling  the holders to purchase or otherwise
acquire Common Stock have been duly authorized and validly  issued.  None of the
outstanding  shares  of  Common  Stock  or  options,  warrants  and  other  such
securities  has  been  issued  in  violation  of the  preemptive  rights  of any
securityholder  of Debtor.  The offers  and sales of the  outstanding  shares of
Common Stock and options, warrants and other rights to acquire Common Stock were
at all relevant times either  registered under the Securities Act and applicable
state securities laws or exempt from such  requirements.  Except as set forth on
Schedule  2.7(d),  there are no stockholders  agreements,  voting  agreements or
other similar  agreements  with respect to the Common Stock to which Debtor is a
party.  Except as set forth on  Schedule  2.7(d),  no holder of any of  Debtor's
securities has any rights,  "demand,"  "piggy-back"  or otherwise,  to have such
securities  registered  by  reason  of  Debtor's  intention  to file,  filing or
effectiveness of the registration  statement on Form SB-2, Form S-1 or Form S-3,
if applicable,  or such successor forms,  registering the shares of Common Stock
for resale.

                  (e) Debtor  has  furnished  to the  Secured  Parties  true and
correct  copies of  Debtor's  Certificate  of  Incorporation,  as amended and in
effect on the date hereof ("Certificate of Incorporation"), and Debtor's Bylaws,
as in effect on the date hereof (the "Bylaws").

         Section 2.8       SEC Documents; Financial Statements.

                  (a) Debtor has timely  filed all  reports,  schedules,  forms,
statements and other documents  required to be filed by it with the SEC pursuant
to the reporting requirements of the Securities Exchange Act of 1934, as amended
(the "Exchange Act") and any other material reports or documents  required to be
filed  with the SEC.  Debtor  has  delivered  to the  Secured  Parties,  or made
accessible to the Secured  Parties,  true and complete copies of documents filed
with the SEC, except for documents or portions of such documents that Debtor has
been granted or is seeking confidential treatment. As of their respective dates,
the  documents  filed with the SEC  complied in all material  respects  with the
requirements  of the  Exchange  Act and the  rules  and  regulations  of the SEC
promulgated  thereunder  applicable to the documents,  and none of the documents
filed  with the SEC,  at the time they were filed  with the SEC,  contained  any
untrue statement of a material fact or omitted to state a material fact required
to be stated therein,  or necessary in order to make the statements  therein, in
light of the circumstances under which they were made, not misleading.

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                  (b) As of their respective dates, the financial  statements of
Debtor  included in the documents  filed with the SEC complied as to form in all
material  respects with  applicable  accounting  requirements  and the published
rules and regulations of the SEC with respect thereto. Such financial statements
have  been  prepared  in  accordance  with  United  States  generally   accepted
accounting  principles  ("GAAP"),   consistently  applied,  during  the  periods
involved (except (1) as may be otherwise indicated in such financial  statements
or the notes thereto, or (2) in the case of unaudited interim statements, to the
extent they may not include footnotes or may be condensed or summary statements)
and fairly present in all material respects, the consolidated financial position
of Debtor and its  consolidated  subsidiaries,  as of the dates  thereof and the
consolidated  results of their  operations  and cash flows for the periods  then
ended (subject,  in the case of unaudited  statements,  to normal year-end audit
adjustments).  The unaudited pro forma combined financial  statements filed with
the SEC comply in all material  respects with the  requirements of Article 11 of
Regulation S-X under the Securities Act.

         Section 2.9 No  Conflicts.  Except as set forth in Schedule  2.9 of the
Disclosure Schedule, the execution,  delivery and performance of this Agreement,
the Loan Agreement,  the  Registration  Rights Agreement and the Notes by Debtor
and the  consummation  by Debtor of the  transactions  contemplated  hereby  and
thereby will not (i) conflict  with or result in a violation of any provision of
the  Certificate  of  Incorporation  or the Bylaws,  or (ii) violate or conflict
with,  or result in a breach of any provision of, or constitute a default (or an
event which with notice or lapse of time or both could become a default)  under,
or  give to  others  any  rights  of  termination,  amendment,  acceleration  or
cancellation  of, any agreement,  indenture or instrument to which Debtor or any
of its  subsidiaries  is a party,  or result in a  violation  of any law,  rule,
regulation,  order,  judgment or decree (including  federal and state securities
laws and  regulations)  applicable  to Debtor or any of its  subsidiaries  or by
which any  property  or asset of Debtor or any of its  subsidiaries  is bound or
affected.  Neither  Debtor nor any of its  subsidiaries  is in  violation of its
certificate of incorporation,  bylaws or other organizational documents.  Except
as set forth in Schedule 2.9 of the Disclosure Schedule,  neither Debtor nor any
of its  subsidiaries is in default,  and no event has occurred which with notice
or lapse of time or both could put Debtor or any of its subsidiaries in default,
under,  and neither Debtor nor any of its  subsidiaries  has taken any action or
failed to take an action  that would  give to others any rights of  termination,
amendment,  acceleration or cancellation  of, any agreement,  indenture or other
instrument to which Debtor or any of its subsidiaries is a party or by which any
property or assets of Debtor or any of its  subsidiaries  is bound or  affected,
except for possible  defaults as would not,  individually  or in the  aggregate,
have a Material  Adverse  Effect.  Except as  specifically  contemplated by this
Agreement,   the  Registration  Rights  Agreement  and  as  required  under  the
Securities Act and any applicable state securities laws,  Debtor is not required
to  obtain  any  consent,  authorization  or order  of,  or make any  filing  or
registration  with,  any  court or  governmental  agency  or any  regulatory  or
regulatory  agency in order for it to  execute,  deliver or  perform  any of its
obligations under this Agreement,  the Loan Agreement,  the Registration  Rights
Agreement  or the Notes in  accordance  with the terms  hereof or  thereof.  All
consents,  authorizations,  orders,  filings and  registrations  which Debtor is
required to obtain  pursuant to the  preceding  sentence  have been  obtained or
effected on or prior to the date hereof. Debtor and its subsidiaries are unaware
of any facts or circumstances which might give rise to any of the foregoing. For
purposes of this  Agreement,  "Material  Adverse  Effect"  shall mean a material
adverse effect on (i) the business,  operations,  affairs,  financial condition,
assets or properties of Debtor or any of its  subsidiaries,  or (ii) the ability
of Debtor to perform the obligations  under this Agreement,  the Loan Agreement,
the  Registration  Rights  Agreement  or the  Notes,  or (iii) the  validity  or
enforceablity of this Agreement,  the Loan Agreement,  the  Registration  Rights
Agreement  or the  Notes  or (d) the  validity  or  perfection  of the  security
interests granted under and pursuant to this Agreement.

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                       Affirmative and Negative Covenants

         Debtor  covenants  and agrees with the Secured  Parties that so long as
the Notes are outstanding:

         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
the Prior Secured  Parties and the Secured Parties  hereunder,  and shall defend
Debtor's rights in the Collateral and the Secured Parties'  security interest in
the  Collateral  against  the claims of all  others,  except  the Prior  Secured
Parties.

         Section 3.3  Modification  of  Collateral.  Debtor  shall do nothing to
impair the rights of the Secured  Parties in the  Collateral.  Without the prior
written consent of the Secured Parties,  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 the Secured  Parties,  other than in the ordinary  course of
business of Debtor and its subsidiaries.

         Section 3.5 Further Assurances. At any time and from time to time, upon
the request of the Secured  Parties,  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 the Secured Parties or the Collateral  Agent may
deem  reasonably  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  the   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.  Debtor hereby
authorizes  the  Collateral  Agent  to file  one or more  financing  statements,
continuation  statements  and  amendments  thereto,   relating  to  any  of  the
Collateral,  without the  signature  of Debtor;  provided  that Debtor  shall be
provided with a copy of such statements and amendments  immediately prior to the
filing or recording thereof.

         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 similar
business,  and (ii) insuring  Debtor,  the Prior Secured Parties and the Secured
Parties  against  liability for personal  injury and property damage relating to
the  Collateral and the operation of Debtor's  business,  such policies to be in
such  amounts and  covering  such risks as are  customarily  insured  against by
companies  engaged  in the same or  similar  business,  with  losses  payable to
Debtor,  the Prior Secured Parties and the Secured  Parties as their  respective
priority  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 the Secured Parties and the Collateral  Agent

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have  received  thirty (30) days prior  written  notice  thereof.  Debtor  shall
deliver to the Collateral  Agent copies of all insurance  policies  covering the
Collateral  or any part thereof upon  request.  In addition,  Debtor shall cause
Probex Fluids Recovery,  Inc., a Delaware corporation and Debtor's  wholly-owned
subsidiary,  to maintain  insurance  policies in such amounts and covering  such
risks as are  customarily  insured  against by companies  engaged in the same or
similar business.

         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 New
York).

         Section 3.8 Inspection Rights.  Debtor shall permit the Secured Parties
and their  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 the Secured Parties 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 the Secured
Parties  and  the  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.   Debtor  shall  not  change  its  state  of
incorporation, principal place of business, chief executive office, or the place
where it keeps its books and  records  unless it shall  have  given the  Secured
Parties  thirty (30) days prior written  notice thereof and shall have taken all
action deemed reasonably  necessary or desirable by the Secured Parties to cause
the  security  interest in the  Collateral  to be  perfected  with the  priority
required  by  this  Agreement.   Debtor  shall  not  amend  its  Certificate  of
Incorporation,  except as necessary to effect the Qualified Equity Financing (as
defined in the Notes) and Wellsville Financing (as defined below).

         Section 3.13 Books and Records. 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 mark its books and  records to reflect the
security interest of the Secured Parties under this Agreement.

         Section 3.14 Information. Debtor shall from time to time at the request
of the Secured Parties deliver to the Secured Parties such information regarding
the  Collateral and Debtor,  to the extent  publicly  disclosed,  as the Secured
Parties  may  reasonably  request,  including,  without  limitation,  lists  and
descriptions of the Collateral and evidence of the identity and existence of the
Collateral.  The Secured  Parties  shall have ready access to all  documentation
related to the proposed  Qualified  Equity Financing and related to the proposed
Wellsville project debt financing ("Wellsville Financing"), either by electronic
means or such other reasonable delivery method, and the Secured Parties shall be
afforded a reasonable  opportunity to comment on the Qualified  Equity Financing
and  Wellsville  Financing  documents;  provided,  however,  Debtor shall not be

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obligated to accept any comments by the Secured  Parties or, with respect to the
Wellsville Financing  documents,  delay the completion of such documents for the
Secured Parties'  comments,  if any. The Secured Parties shall have the right to
participate in meetings with Debtor's  financial advisors or other third parties
related to the Qualified  Equity Financing and Wellsville  Financing;  provided,
however,  that  participation  in meetings  other than "all hands" or comparable
meetings  by the  Secured  Parties is subject to mutual  agreement  between  the
Secured Parties and Debtor.

         Section 3.15  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  3.16  Compliance  with  Laws.  Debtor  shall  comply  with all
applicable  laws,  rules,  regulations,  and orders of any court or governmental
authority.

         Section 3.17 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 the Collateral Agent.

         Section 3.18 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 the Secured Parties;  provided,  however, the foregoing shall
not  limit  Debtor's  or its  subsidiaries'  ability  to  license  or  otherwise
distribute the  Intellectual  Property in the ordinary  course of business while
retaining its ownership interest therein.

         Section 3.19 Additional Indebtedness. So long as any of the Obligations
remain  outstanding,  neither Debtor nor any of its subsidiaries shall incur any
additional  indebtedness for borrowed money, other than indebtedness of not less
than $80 million in principal amount used to finance Debtor's  proposed facility
in Wellsville,  Ohio, or grant any liens, mortgages or other security interests,
in each case without the prior consent of the Secured Parties.

         Section 3.20 Merger; Consolidation. Debtor and each of its subsidiaries
shall not consolidate with or merge with any other entity or convey, transfer or
lease all or substantially  all of its assets in a single  transaction or series
of transactions to any person.

         Section 3.21 Limitations on Restricted Payments.  Debtor shall not, and
will not permit any of its subsidiaries to:

                  (a)      declare  or pay  any  dividends,  either  in  cash or
                           property,  on  Common  Stock,  except  (i)  dividends
                           payable  solely in  shares  of common  stock or other
                           equity interests of Debtor and (ii) dividends payable
                           by a  wholly-owned  subsidiary of Debtor to Debtor or
                           to another wholly-owned subsidiary of Debtor; or

                  (b)      directly  or  indirectly,  or through any of Debtor's
                           subsidiaries  or  through  any  affiliate  of Debtor,
                           purchase,  redeem or retire  any  shares of  Debtor's
                           capital stock of any class or other equity  interests
                           or any  warrants,  rights or options to  purchase  or
                           acquire  any shares of Common  Stock or other  equity
                           interests  of Debtor  (other than in exchange  for or
                           out  the  net  cash   proceeds  to  Debtor  from  the
                           substantially  concurrent  issue or sale of shares of
                           Common Stock or other  equity  interests of Debtor or
                           warrants,  rights or options to  purchase  or acquire
                           any shares of Common Stock or other equity  interests
                           of Debtor).

                                       7
<PAGE>


         Section 3.22 Limitations on Guarantees. Except as in effect on the date
hereof,  Debtor shall not  guarantee or otherwise in any manner become liable in
respect of any debt or liability of any other person.

         Section 3.23  Limitations on Investment.  Neither Debtor nor any of its
subsidiaries  shall make any investments,  loans or advances to any person other
than Debtor (including, without limitation, any of Debtor's subsidiaries), other
than loans or  advances  to  officers,  directors  and  employees  for  expenses
(including  moving  expenses  related to a  transfer)  incidental  to and in the
ordinary course of the business of Debtor or any of its subsidiaries.

         Section 3.24 Limitations on Securities  Issuance.  So long as the Notes
remain outstanding, upon the issuance of an aggregate of two million (2,000,000)
shares of Common Stock by Debtor from the date  hereof,  Debtor shall notify the
Secured Parties prior to each issuance of shares of Common Stock thereafter.  So
long as the Notes remain outstanding,  upon the issuance of an aggregate of five
million  (5,000,000)  shares of Common  Stock by  Debtor  from the date  hereof,
Debtor shall not issue any  additional  shares of Common Stock without the prior
written  consent of the Secured  Parties.  For  purposes of this  Section  3.24,
shares of Common  Stock  issued  in  accordance  with the terms of the Notes and
Debtor's  securities  issued to consummate  the Qualified  Equity  Financing and
Wellsville Financing shall not be included.

                      Rights of Secured Parties and Debtor

         Section 4.1 Power of Attorney.  DEBTOR HEREBY  IRREVOCABLY  CONSTITUTES
AND APPOINTS THE 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 THE 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.  Neither  the  Secured  Parties,  Zesiger  Capital  Group,  LLC
("Zesiger")  nor the  Collateral  Agent  shall be under any duty to  exercise or
withhold  the  exercise of any of the rights,  powers,  privileges,  and options
expressly  or  implicitly  granted  to  the  Secured  Parties,  Zesiger  or  the
Collateral  Agent in this Agreement,  and shall not be liable for any failure to
do so or any delay in doing so.  Neither  the Secured  Parties,  Zesiger nor the
Collateral  Agent  shall be liable for any act or  omission  or for any error of
judgment  or any mistake of fact or law in their  individual  capacity or in the
Collateral  Agent's or  Zesiger's  capacity as  attorney-in-fact  except acts or
omissions  resulting  from their willful  misconduct.  This power of attorney is
conferred on the Collateral Agent solely to protect,  preserve, and realize upon
the Secured Parties' security interest in the Collateral.

         Section  4.2  Secured  Parties'  Duty of Care.  The  Collateral  Agent,
Zesiger  and the  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, as against Debtor, the Collateral Agent and the
Secured Parties shall be conclusively  deemed to have exercised  reasonable care
in the custody of the Collateral,  if the Collateral Agent or any of the Secured
Parties take such action,  for purposes of preserving  rights in the Collateral,
as Debtor may  request in  writing,  but no failure or  omission or delay by the
Collateral  Agent or the Secured  Parties in complying  with any such request by
Debtor,  and no refusal by the Collateral Agent or the Secured Parties to comply
with any such  request  by Debtor,  shall be deemed to be a failure to  exercise
reasonable care.

                                       8
<PAGE>


                                     Default

         Section 5.1 Rights and  Remedies.  If any event of default  shall occur
under either the Notes or this Agreement,  the Collateral  Agent and the Secured
Parties  shall have all of the rights and remedies of secured  parties under the
Uniform  Commercial  Code as in  effect  by the State of New York as well as any
other rights and remedies permitted under or provided by applicable law, subject
in all respects to the rights of the Prior Secured Parties.

                         Agreement Among Secured Parties

         Section 6.1 Financing Statement. The 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 Agreement  Among Secured  Parties  Listed On Exhibit C. The
Secured Parties listed on Exhibit C attached hereto hereby appoint,  empower and
authorize  Zesiger  to act  their  attorney-in-fact  for  the  sole  purpose  of
effecting  consents,   requests,  waivers  and  amendments  under  and  to  this
Agreement.

         Section 6.3 Agreement Among All Secured  Parties.  The Collateral Agent
agrees  to act as  collateral  agent  for the  Secured  Parties  hereunder.  The
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 relating to the Collateral.  Each Secured Party also hereby
appoints and authorizes  the  Collateral  Agent to take such actions as agent on
its behalf as are necessary to enforce the Secured  Parties  rights and exercise
their powers under this Agreement; provided, however, the Collateral Agent shall
take such actions and exercise such powers only as and in the manner agreed from
time to time by the  holders  of  two-thirds  (2/3) of the  aggregate  principal
amount of the Notes outstanding on the date thereof; provided, further, however,
that the  Collateral  Agent  shall not be  required  to take any action  that is
contrary  to this  Agreement,  the  Notes or  applicable  law.  Upon an Event of
Default (as defined in the Notes) or Events of Default, such Event of Default or
Events of Default may be waived,  but only by the holders of two-thirds (2/3) of
the aggregate  principal amount of the Notes outstanding on the date thereof. If
the Event of  Default,  or Events of  Default,  are not waived by the holders of
two-thirds (2/3) of the aggregate  principal amount of the Notes  outstanding on
the date thereof, any holder of the Notes shall have the right to accelerate all
of the Notes outstanding on the date thereof in accordance with the terms of the
Notes.

         Section  6.4 Pro Rata  Sharing.  If one of the  Secured  Parties  shall
obtain any payment or funds with respect to any Obligations, 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 each of the other Secured
Parties  its pro rata share of such  excess  payment  or funds,  and each of the
Secured  Parties shall  reallocate  such funds pro rata among all of the Secured
Parties.  If all or a portion of any payment  received by one of Secured Parties
with respect to any  Obligations 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,  each of the other Secured Parties shall pay such Secured Party
its pro rata share of such recovered payment.

         Section  6.5  Enforcement.  Upon  enforcement  and  collection  of  the
Obligations in whole or in part under this  Agreement,  the Secured Parties will
share pro rata in the proceeds  resulting from such  collections  based upon the
ratio of the amount due and owing to the Secured Parties under their  respective
Notes to the aggregate amount due and owing under all of the Notes.

                                       9
<PAGE>

                                  Miscellaneous

         Section 7.1 No Waiver;  Cumulative Remedies.  No failure on the part of
the Collateral  Agent or any of the 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 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 the  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 the Secured Parties.

         Section 7.3 Amendment; Entire Agreement. THIS AGREEMENT,  INCLUDING THE
EXHIBITS AND SCHEDULES  ATTACHED  HERETO,  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 or, in the case
of a mailed notice,  three (3) 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 enforced,  governed by and construed in accordance with the laws of the
State of New York  applicable  to agreements  made and to be performed  entirely
within such State  excepting its choice of law rules,  other than Section 5-1401
of New York's General Obligation Law.

         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;   Schedules.   The   headings,   captions  and
arrangements  used in this  Agreement  are for  convenience  only and  shall not
affect the  interpretation  of this  Agreement.  The  Disclosure  Schedules  and
exhibits  attached  hereto are as fully a part of this Agreement as if set forth
herein in full.

                                       10
<PAGE>


         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/ Bruce A. Hall
Dallas, Texas 75240                     -----------------------------------
Attn: Bruce A. Hall, CFO             Name:  Bruce A. Hall
Facsimile:  (972) 980-8545           Title:  Senior Vice President













                                       11
<PAGE>




                                           SECURED PARTIES:
                                           ---------------


Address:                                   UNITED INFRASTRUCTURE COMPANY, LLC,
                                           a Delaware limited liability company


United Infrastructure Company, LLC
50 California Street, Suite 2200           By: /s/ Nora A. Blum
San Francisco, California 94111               ------------------------------
Attn:  Chief Operating Officer                 Nora A. Blum
Facsimile:  (415) 768-3491                     Vice President



                                            SECURED PARTIES LISTED ON EXHIBIT C
                                            HERETO

Address:                                    By: Zesiger Capital Group, LLC,
                                                as agent and attorney-in-fact
c/o Zesiger Capital Group, LLC
320 Park Avenue, 30th Floor
New York, NY, 10022                             By:/s/ Lisa W. Hess
Attn:  Albert L. Zesiger                           ---------------------------
Facsimile: 212-508-6329                         Name: Lisa W. Hess
                                                Title:


                                            COLLATERAL AGENT:
                                            ----------------

Address:                                    UNITED INFRASTRUCTURE COMPANY, LLC,
                                            a Delaware limited liability company


United Infrastructure Company, LLC
50 California Street, Suite 2200            By: /s/ Nora A. Blum
San Francisco, California 94111                --------------------------------
Attn:  Chief Operating Officer                 Nora A. Blum
Facsimile:  (415) 768-3491                     Vice President





                  SCHEDULES AND EXHIBITS INTENTIONALLY OMITTED.




                                       12