Document:

<PAGE>

                                                                   EXHIBIT 10.35

                  SECOND AMENDMENT TO INVESTOR RIGHTS AGREEMENT

      This SECOND AMENDMENT TO INVESTOR RIGHTS AGREEMENT (the "Second
Amendment") is made as of this 26th day of April, 2002 by and among Probex
Corp., a Delaware corporation with its chief executive office located at One
Galleria Tower, 1335 Noel Road, Suite 1200, Dallas, TX 75204 (the "Company") and
HSB Engineering Finance Corporation, a Delaware corporation with its chief
executive office located at One State Street Hartford, Connecticut 06102-5024
(the "Investor").

                                   WITNESSETH:

      WHEREAS, Alex D. Daspit, Martin R. MacDonald and Thomas G. Murray,
individuals residing in the State of Texas (collectively, the "Shareholders"),
the Company and Investor entered into that certain Investor Rights Agreement
dated as of the 30th day of June, 1998 (the "Agreement") whereby the Company
granted certain rights to the Investor in connection with a loan made by the
Investor to the Company; and

      WHEREAS, the Investor, the Company and the Shareholders amended and
restated the Agreement pursuant to that certain Amended and Restated Investor
Rights Agreement dated as of the 2nd day of June, 2000 (the "Prior Amendment");
and

      WHEREAS, the Investor and the Company desire to further amend the
Agreement; and

      WHEREAS, Section 6.2 of the Agreement provides that no modification or
amendment of the Agreement shall be effective unless the same shall be in
writing and signed by the Company and the Investor;

      NOW, THEREFORE, in consideration of the mutual covenants set forth herein
and other good and valuable consideration, the receipt and sufficiency of which
is hereby acknowledged, the Investor and the Company agree as follows:

      1.    Amendment of Agreement. The Investor and the Company hereby agree to
amend the Agreement by repealing Section 2 of the Agreement, entitled "Voting
Agreement" in its entirety and inserting the following in lieu thereof as a new
Section 2, entitled "Board Observer Rights":

"The Investor shall have the following rights:

            (a)   Notices, etc. The Investor shall be given a copy of any and
all notices or other written materials sent to the Company's Board of Directors
(the "Board"`) at the same time as such materials are given to the members of
the Board, including without limitation notices of
<PAGE>
                                      -2-

meetings, written consents to be signed by members of the Board, financial or
other reports and materials related to the meeting of Board committees.

            (b)   Observation Rights. The Investor shall have the right to have
a representative attend any meetings of the Board (including any adjournments
thereof) either in person or by telephone. Notwithstanding any implication to
the contrary contained herein, no meeting of the Board shall be conducted
unless, in the case of special meetings, such representative of the Investor
shall have been given prior written notice of such meeting in accordance with
the notice requirements of the Company's bylaws applicable to the directors of
the Company and, in the case of regular meetings, the Company has used its
reasonable efforts to provide the representative of the Investor at least 24
hours' notice but, in any event, has given such representative at least as much
actual notice as has been provided to other members of the Board. Such
representative shall have the right to speak at such meetings and to make such
suggestions and requests during such meetings as such representative deems
appropriate. The Board shall take no action to exclude such representative from
any such meeting or to conduct any such meeting in executive session or
otherwise to the exclusion of such representative unless the Board determines,
in the exercise of its reasonable business judgement, that such exclusion is in
the best interests of the Company and its shareholders. The Company shall
reimburse the Investor's representative for costs incurred in connection with
any Board meeting to the same extent that it reimburses Board members for such
costs. Exercise of the rights granted in this subsection (b) shall not be, and
shall not be deemed to be, participation by the Investor on the Board.

            (c)   Expiration. The rights granted to the Investor in this Section
2 shall expire at such time as (i) the Investor, together with its Affiliates
(as defined in the Loan Agreement), in the aggregate holds Common Stock
representing less than 5% of the outstanding Common Stock of the Company and
(ii) all Company securities held by the Investor or its Affiliates may be freely
sold to the public pursuant to a registration under the Securities Act (as such
term is defined in Section 3.1) (which, at such time, is already filed and in
place)."

      2.    Effect of Amendment. The Investor, the Company and the Shareholders
hereby agree and acknowledge that except as provided in this Second Amendment,
the Agreement (as amended by the Prior Amendment) remains in full force and
effect and has not been modified or amended in any respect, it being the
intention of the Investor, the Company and the Shareholders that this Second
Amendment and the Agreement (as amended by the Prior Amendment) be read,
construed and interpreted as one and the same instrument.

      3.    Capitalized Terms. All capitalized terms not otherwise defined in
this Second Amendment shall have the meanings ascribed to such terms in the
Agreement (as amended by the Prior Amendment).
<PAGE>
                                      -3-

      IN WITNESS WHEREOF, the Investor, the Company and the Shareholders have
executed this Second Amendment as of the date first above written.

PROBEX CORP.                                HSB ENGINEERING FINANCE
                                            CORPORATION

By:    /s/ Charles M. Rampacek              By:    /s/  Saul Basch
     ------------------------------------        -------------------------------
Name:    Charles M. Rampacek                Name:
       ----------------------------------          -----------------------------
Title    President & CEO                    Title:
       ----------------------------------           ----------------------------<PAGE>

                                                                   EXHIBIT 10.36

                        Columbiana County Port Authority
               1250 St. George Street, East Liverpool, Ohio 43920
                       (330) 386-9051 - FAX (330) 386-1122

May 29, 2002

Martin MacDonald                                            Via E-Mail
Senior VP of Technology & Business Development
PROBEX
One Galleria Tower
13355 Noel Rd, Suite 1200
Dallas Texas, 75240

Dear Martin:

This letter is to confirm that the Columbiana County Port Authority will grant
to Probex an extension of the Wellsville Site Option to Purchase Agreement
through November 30, 2002. As compensation for grant of the extension, please
remit $20,000.00 to the Port Authority prior to June 15, 2002. This amount will
be in addition to the continuing monthly fees due under the Agreement.

                                    Yours truly,

                                    /s/ Tracy V. Drake

                                    Tracy V. Drake
                                    Executive Director

TVD/sls
<PAGE>
                        Columbiana County Port Authority
               1250 St. George Street, East Liverpool, Ohio 43920
                       (330) 386-9051 - FAX (330) 386-1122

July 17, 2000

Martin R. MacDonald
Senior Vice President
Operations
Probex Corporation
1467 LeMay, Suite 111
Carrollton, Texas 75007

Dear Martin:

Please find enclosed an executed Extension of Option document. We are standing
by to receive PROBEX's check for $15,000.00.

                                    Yours truly,

                                    /s/ Tracy V. Drake

                                    Tracy V. Drake
                                    Executive Director

TVD/jlb
<PAGE>
                               EXTENSION OF OPTION

      This Extension of Option Agreement is entered into as of this 19th day of
June, 2000, by and between COLUMBIANA COUNTY PORT AUTHORITY, a body corporate
and politic, (the AUTHORITY) and PROBEX CORPORATION, a Colorado corporation, or
its assignee (Probex).

      WITNESSETH:

      WHEREAS, the AUTHORITY and PROBEX heretofore entered into that certain
Option Purchase Agreement, as finally executed by the parties on July 7, 1999
(copy attached); and,

      WHEREAS, the AUTHORITY is desirous in granting to PROBEX and PROBEX is
desirous of obtaining from the AUTHORITY, an extension of the aforesaid
described Option to Purchase.

      NOW, THEREFORE, in consideration of the following, the parties do hereby
agree as follows:

      (1)   The AUTHORITY does hereby extend the Option period for a period of
            six (6) months from the 1st day of July, 2000, through the 31st day
            of December, 2000.

      (2)   PROBEX shall, on July 1, 2000, pay the sum of Five Thousand Dollars
            ($5,000) to the AUTHORITY. Said $5,000 payment shall not be credited
            to PROBEX toward the purchase price, if PROBEX exercises such
            Option.

      (3)   PROBEX shall also on the 1st day of each and every month, commencing
            July 1, 2000 pay the monthly sum of Ten Thousand Dollars ($10,000)
            for each month of this Option Extension until such Option is
            exercised or cancelled by Probex. If said Option is exercised, then
            all monthly options payments made shall be credited toward the
            purchase price. If, however, said Option is not exercised, or is
            cancelled by Probex, then all monthly Option payments made shall
            remain the sole property of the AUTHORITY.

      (4)   Probex shall have the right, exercisable in its sole discretion, to
            cancel the Option to Purchase upon written notice to the AUTHORITY.
            Such cancellation shall terminate Probex's obligations to make any
            future monthly option payments.

      (5)   All other terms and conditions of the existing Option to Purchase,
            as signed by the parties on June 28, 1999, and July 7, 1999, shall
            continue to remain in full force and effect.

Wells04.009                            1                                7/6/00
<PAGE>
IN WITNESS WHEREOF, the parties hereto have caused this agreement to be finally
executed and delivered as of the effective dates below.

PROBEX:                                THE AUTHORITY:

Probex Corporation,                    Columbiana County Port Authority,
A Colorado corporation                 A body corporate and politic

BY:  /s/ M R MacDonald                 BY:  /s/ Tracy V. Drake
   ------------------------------         ------------------------------------

NAME:  MARTIN MacDONALD                NAME:  TRACY V. DRAKE

TITLE: SENIOR VICE PRESIDENT           TITLE: EXECUTIVE DIRECTOR
       OPERATIONS

DATE:     07/07/00                     DATE:      7/17/00
     ----------------------------           ----------------------------------

Wells04.009                            2                                7/6/00
<PAGE>
                        Columbiana County Port Authority
               1250 St. George Street, East Liverpool, Ohio 43920
                       (330) 386-9051 - FAX (330) 386-1122

July 2, 1999

Martin McDonald
PROBEX
1467 LeMay, Suite 111
Carrollton, Texas 75007

Dear Martin:

Please find attached three (3) original Option to Purchase Agreements. Please
sign all three, keep one copy for your files and return two (2) originals to the
Port Authority. I will forward one (1) original to Atty. Mike Kapp for his
files.

If you have any questions, please give me a call.

                                    Yours truly,

                                    /s/ Sandy Steele

                                    Sandy Steele
                                    Executive Assistant

/sls
<PAGE>
                                  RESOLUTION OF

                             THE BOARD OF DIRECTORS

                                       OF

                 THE PORT AUTHORITY FOR COLUMBIANA COUNTY, OHIO

      BE IT RESOLVED BY THE BOARD OF DIRECTORS OF THE PORT AUTHORITY FOR
COLUMBIANA COUNTY:

      SECTION ONE: That the Port Authority for Columbiana County, Ohio, enter
into that certain Option to Purchase Agreement with PROBEX CORPORATION. A copy
of said Agreement is attached and made a part of this Resolution as if fully
written herein.

      SECTION TWO: That said Option to Purchase and said Lease Agreement shall
contain such other provisions as are recommended by the legal counsel for the
Port Authority, consistent with the provisions of said Option to Purchase.

      SECTION THREE: That the Chairman of the Board of Directors of the Port
Authority for Columbiana County, or the Vice Chairman, or the Executive
Director, be and he is hereby authorized to execute said Lease Agreement on
behalf of the Port Authority.

      BE IT FURTHER RESOLVED that it is found and determined that all formal
actions of this Board concerning and relating to the adoption of this resolution
were adopted in an open meeting of this Board, and that all deliberations of
this Board that resulted in such formal action, were in meetings open to the
public, in compliance with all legal requirements, including Section 121.22 of
the Ohio Revised Code.
<PAGE>
                               OPTION TO PURCHASE

      THIS OPTION TO PURCHASE OR LEASE (this "Agreement") is entered into as of
June __, 1999, by and between Columbiana County Port Authority, a body corporate
and politic (the "Authority"), and Probex Corporation, a Colorado corporation,
or its assignee ("Probex").

                                   WITNESSETH:

      WHEREAS, the Authority is the owner of certain real property located in
Columbiana County, Ohio (the "Property"), more particularly described on Exhibit
A attached hereto and made a part hereof for all purposes; and

      WHEREAS, the Authority is desirous of granting to Probex and Probex is
desirous of obtaining from the Authority, the exclusive, irrevocable right and
option to purchase the Property pursuant to the terms and conditions of the
Agreement for the purposes of erecting a used oil re-refining plant (the
"Facility").

      NOW, THEREFORE, in consideration of $5,000, as well as approximately
$100,000 in expenses to be incurred by Probex with respect to this Agreement,
the Property, and the Facility during the Option Period (defined below) and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged by the Authority, the premises and the following mutual
covenants and agreements, the parties hereto covenant and agree as follows:

                                    ARTICLE I
                                GRANT OF OPTIONS

      Section 1.01. Grant of Purchase Option. (a) Upon and subject to the terms
and conditions set forth in this Agreement, the Authority hereby grants and
conveys to Probex the exclusive, irrevocable right and option to purchase the
Property (the "Purchase Option") for a purchase price (the "Purchase Price") of
$1,350,000.00. (b) The Authority shall use its best efforts (i) to purchase, at
a competitive price acceptable to Probex, the approximately 4.2 acres of
property owned by Norfolk Southern described on Exhibit B attached hereto and
made a part hereof for all purposes (the "Norfolk Southern Property") and (ii)
to obtain the release of any easements owned by Norfolk Southern which burden
the property. If the Authority is successful in so purchasing the Norfolk
Southern Property, then the Norfolk Southern Property shall automatically be a
part of, and shall be included within the definition of, "Property" for all
purposes and shall be burdened by this Agreement, except that Probex shall be
responsible for the cost of the Norfolk Southern Property paid by Port Authority
if Probex elects to purchase such property from Authority. (c) The purchase and
sale of the Property pursuant to any exercise of the Purchase Option shall be
subject to the terms and conditions set forth herein and in a purchase agreement
(the "Purchase Agreement") substantially in the form attached hereto which shall
be more fully negotiated in good faith by the Authority and Probex prior to the
consummation of such purchase and sale of the Property.
<PAGE>
      Section 1.02. Interim Lease. The "Property" and certain other immediate
surrounding land will be improved by construction of an adjacent highway
primarily using Federal funds. The Federal Highway Administration has determined
that no transfers of title to such land to private industry may take place prior
to completion of the interchange which is projected to occur on or before the of
the end of the second quarter of the Calendar Year 2001. In the event Probex
chooses to exercise the Purchase Option, then an Interim Lease shall
automatically then be deemed to be in effect between the parties which shall
remain in effect until Authority certifies to Probex in writing that the
interchange is complete. Rental payments under the Interim Lease shall be Twenty
Thousand Dollars ($20,000.00) per month which payments in total shall be
credited against the Purchase Price. Other terms and conditions of the Interim
Lease are set forth in Exhibit C attached hereto and made a part hereof for all
purposes. Closing on the Purchase shall occur in the offices of Authority within
20 business days of Authority's notice to Probex that the interchange is
complete.

      Section 1.03. Term of the Option. The Purchase Option shall commence on
the date of this Agreement and shall continue until 5:00 p.m. Central Time
twelve (12) months from the date of this Agreement (the "Option Period").

      Section 1.04. Exercise of the Option. Probex may exercise the Purchase
Option by execution and tender to the Authority of a written notice exercising
such Option. If Probex fails to exercise the Purchase Option in accordance with
the terms of this Agreement within the Option Period then the Options and the
rights thereunder of Probex shall automatically and immediately terminate
without notice.

                                   ARTICLE II
                         DUE DILIGENCE AND TITLE MATTERS

      Section 2.01. Environment Assessments. During the Option Period, Probex,
its agents and contractors, shall have the right to enter upon the Property for
the purpose of conducting inspections and investigations, preparing surveys and
site plans, and performing an environmental assessment of the Property. The
environmental assessment may include, but shall not be limited to subsurface
soil and water tests, as well as the testing of any underground storage tanks
and related equipment upon the Property. Probex shall assume all risks involved
in entering upon the Property for the performance of such activities and shall
indemnify and hold the Authority harmless from and against all loss or expense
by reason of all liability due to bodily injury, death of persons, damage to
property sustained by any party or any damage to the Property arising out of or
caused by such entry by Probex, its agents or contractors or the negligence of
Probex or its agents or contractors in the exercise of any of Probex's rights
under this section. Probex, its agents and contractors, shall also have the
right to make inquiries into or contact with, governmental agencies concerning
potentially hazardous substances on the Property without any liability on the
part of Probex, its agents or contractors, to the Authority as a result thereof.

      Section 2.02. Survey, Title Commitment and Miscellaneous Documents.

      (a)   Within thirty (30) days after the exercise of the Option (and
updated within ninety (90) days) before any consummation of the purchase and
sale or lease of the Property, the
<PAGE>
Authority, with the cost for such expense to be borne equally by the parties,
shall furnish to Probex a currently dated survey (the "Survey") of the Property
prepared and certified by a duly licensed professional engineer or surveyor
reasonably acceptable to Probex and a title company selected by Probex (the
"Title Company") and sufficient to allow the Title Company to delete the survey
exception. The Survey shall reflect the following:

            (i)   A certification to Probex, the Title Company and a lender to
      be designated by Probex to the effect that the Survey (a) was made on the
      ground as per the field notes shown thereon and correctly shows the
      boundary lines and dimensions and the area of the Property (or any
      separate parcels thereof), (b) correctly shows the location of all
      buildings, structures, and other visible improvements on the Property, (c)
      correctly shows the location and dimensions of all alleys, streets, roads,
      rights-of-way, easements, and other matters of record of which the
      surveyor has been advised affecting the Property according to the legal
      description in such easements and outer matters (with instrument, book,
      and page number indicated), (d) except as shown, no portion of the
      Property is located within a special flood hazard area, (e) there are no
      visible easements, rights-of-way, party walls or conflicts, (f) there are
      no visible encroachments or adjoining premises, streets, or alleys by any
      of said buildings, structures, or other improvements, (g) there are no
      visible encroachments on the Property by buildings, structures, or other
      improvements situated on adjoining premises; and (h) the distance from the
      nearest intersecting street and road is as shown thereon;

            (ii)  The location of all improvements, street, highways,
      rights-of-ways and easements appurtenant to, traversing, adjoining or
      bounding the Property (which shall show all applicable recording data);

            (iii) Any encroachments on the Property or protrusions on adjacent
      land;

            (iv)  A metes and bounds description of the Property and the total
      acres contained therein;

            (v)   The beginning point should be established by a monument
      located at the beginning point, or by reference to a nearby monument;

            (vi)  A legally sufficient description for all necessary easements
      for access to and from the Property to the nearest publicly dedicated road
      or street and for water, storm and sanitary sewer, electricity, gas and
      telephone utility service to the Property; and

            (vii) The boundary line of highways and streets abutting the
      Property and the width of said highways and streets, including any
      proposed relocation, modification or widening thereof.

      (b)   Within thirty (30) days after the exercise for the Purchase Option
and updated within ten (10) days before any consummation of the purchase and
sale of the Property, the Authority, at the Authority's sole cost and expense,
shall cause to be furnished to Probex a current title commitment (a
"Commitment") for an owner's policy of title insurance issued through the Title
Company setting forth the state of title to the Property and all objections or
exceptions thereto including, without limitation, rights-of-way, easements,
restrictions,
<PAGE>
reservations, covenants, liens, encumbrances, estates and other conditions, if
any, affecting the Property which would appear in an owner's policy of title
insurance, if issued. The Authority shall also cause to be furnished to Probex,
at the Authority's sole cost and expense, a copy of all instruments creating
such aforesaid objections or exceptions to title, if any, contemporaneously with
the furnishing of the Commitment.

                                   ARTICLE III
                        PROVISIONS OF GENERAL APPLICATION

      Section 3.01. Commissions. Probex and the Authority warrant and represent
to the other that neither has made any agreements for real estate brokers',
agents' or finders' fees or commissions by reason of the sale of the Property,
the execution of this Agreement or the consummation of the transactions
contemplated herein. Each party hereto hereby agrees to indemnify and hold the
other party harmless from claims made by any person for any such fees or like
compensation arising on account of such party's acts.

      Section 3.02. Condemnation. In the event that any portion or a Property
shall be taken in condemnation or under the right of eminent domain after the
date of the Authority's execution hereof and before the consummation of the
purchase and sale of the Property, this Agreement, at the option of Probex, may
either: (a) be declared null and void and all payments or deposits made
hereunder with respect to the Property shall then immediately be returned to
Probex or (b) the proceeds received from such condemnation or right of eminent
domain proceeding shall be applied against, and pro tanto reduce, the purchase
price hereunder of the Property.

      Section 3.03. Further Instruments. Each party hereto shall from time to
time execute and deliver such further instruments as the other party or its
counsel may reasonably request to effectuate the intent of this Agreement,
including, but not limited to, documents necessary for compliance with the laws,
ordinances, rules or regulations of any applicable governmental authorities.

      Section 3.04. Governing Law. The parties hereto hereby expressly agree
that the terms and conditions hereof, and the subsequent performance hereunder,
shall be constructed and controlled by the laws of the State of Ohio.

      Section 3.05. Headings. Article and Section headings used in this
Agreement are for convenience of reference only and shall not affect the
construction of any provision of this Agreement.

      Section 3.06. Entire Agreement; Alteration of Amendment. This Agreement
constitutes the entire agreement of the parties with respect to the subject
matter hereof. Except as incorporated herein by reference, any and all prior
agreements, whether written or oral are superseded hereby and are deemed null
and void and of no effect. The parties are not bound by any agreements,
understandings, conditions or inducements otherwise than are as expressly
referenced, set forth, or stipulate hereunder. No change, alteration, amendment,
modification or waiver of any of the terms or provisions hereof shall be valid
unless the same shall be in writing and signed by the parties hereto.
<PAGE>
      Section 3.07. Assignment. This Agreement shall be binding upon, and inure
to the benefit of, the Authority and Probex and their respective permitted
successors and assigns. This Agreement shall not be assignable by the Authority.
Probex shall not have the right to assign any or all of its rights or interest
herein without the Authority's prior written approval, which shall not be
unreasonably withheld.

      Section 3.08. Notices. All notices, demands and requests provided for
hereunder shall be deemed given and received (a) when personally delivered; or
(b) on the fifth business day after the same are deposited in the United States
mail, postage prepaid, registered or certified mail, return receipt requested,
addressed to the applicable party at the address indicated below for such party,
or as to each party, at such other address as shall be designated by such party
in a written notice to the other party

      TO THE AUTHORITY:       Columbiana County Port Authority
                              1250 St. George Street
                              East Liverpool, Ohio 43920
                              Attention:  Tracy Drake, Executive Director

      TO PROBEX:              Probex Corporation
                              1467 LeMay Drive, Suite 112
                              Carrollton, Texas 75007-4923
                              Attention:  Martin MacDonald, Vice President
                              Operations

or at such other place as Probex or the Authority may from time to times
designate in written notice pursuant to the terms hereof.

      Section 3.09. Conditions Precedent. Except as other wise modified or
changed by this Agreement, the contingencies and/or conditions contained in that
certain letter dated April 20, 1999, addressed to the Authority from Probex are
incorporated herein by reference thereto and shall be conditions precedent to
performance by the parties under the Purchase Agreement or the Lease Agreement
regardless of whether expressly stated therein. The party for whose benefit a
condition exists may unilaterally waive same.

      Section 3.10. Attorney's Fees. In the event that any party is required to
commence any action or proceeding or against the other concerning the subject
matter of this Agreement, the prevailing party therein shall be entitled to
recover, in addition to any amounts or relief otherwise awarded, all reasonable
costs incurred in connection therewith, including reasonable attorneys' fees.

      Section 3.11. Disclosure for Foreign Investment in Real Property Tax Act.
The Authority shall furnish to Probex on or before the consummation of the
purchase and sale or lease of the Property a sworn Affidavit in form acceptable
to Probex stating under penalty of perjury that the Authority is not a "foreign
person" as such term is defined in Section 1445(f)(3) of the Internal Revenue
Code of 1954, as amended (the "Code") or such other evidence that Probex is not
required to withhold taxes from the purchase price under Section 1445(a) of the
Code as Probex may reasonably determine to meet the requirements of Section
1445(b)(4) and Section 1445(b)(5) of the Code. In the event the Authority does
not furnish the sworn Affidavit or such other evidence deemed satisfactory by
Probex as required by this Section 3.11, Probex
<PAGE>
may withhold (or may direct the Title Company to withhold) from the cash funds
payable to the Authority pursuant to this Agreement, an amount equal to the
amount required to be so withheld pursuant to Section 1445(a) of the Code and
such withheld funds shall be deposited with the Internal Revenue Service as
required by said Section 1445(a) and the regulations promulgated thereunder.

      Section 3.12. Invalidity of Any Provision. In the event that any condition
or covenant herein contained is held to be invalid or void by any court of
competent jurisdiction, the same shall be deemed severable from the remainder of
this Agreement and shall in no way affect any other covenant or condition herein
contained. If such condition, covenant or other provision shall be deemed
invalid due to its scope or breadth, such provision shall be deemed valid to the
extent of the scope or breadth permitted by law.

      Section 3.13. Waiver of Rights. Notwithstanding anything set forth herein
to the contrary, if no notice of a default or waiver is required hereunder and
none has been given, neither party hereto shall be deemed to have waived any
rights which it may have hereunder until forty-eight (48) hours following
receipt by it (the "Waiving Party") of written notice from the other party
alerting the Waiving Party to the fact that the time for exercising any right or
remedy hereunder has elapsed without exercise thereof and such time for exercise
shall automatically be a period which ends forty-eight (48) hours after such
notice or will elapse pursuant to the terms of this Agreement not more than
forty-eight (48) hours following the date such notice. If no action is taken by
the Waiving Party within the forty-eight (48) hour period following such notice,
said right shall conclusively be deemed to have been waived. The Intent of this
section is to avoid unintentional waivers by either party hereto of any of its
rights hereunder.

      Section 3.14. Memorandum of Option. The Authority shall execute and
deliver to Probex a written memorandum of this Agreement which Probex may record
in the state, county or municipality in which the Property is located.

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

PROBEX:                                THE AUTHORITY:

Probex Corporation,                    Columbiana County Port Authority,
A Colorado corporation                 A body corporate and politic

By:  /s/ M. R. MacDonald               By:  /s/ Tracy V. Drake
   ------------------------------         ------------------------------------
Name:    Martin MacDonald              Name:    Tracy V. Drake
     ----------------------------           ----------------------------------
Title:  Executive V.P.                 Title:  Executive Director
      ---------------------------            ---------------------------------
Date:   07/07/99                       Date:   6/28/99
     ----------------------------           ----------------------------------
<PAGE>
                                   EXHIBIT "A"

                              PROPERTY DESCRIPTION

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