Document:

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                                                                  EXHIBIT 4.3.17

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

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

                         PURCHASE PRICE PER SHARE: $2.70

EXPIRATION DATE: 5:00 P.M., DALLAS, TEXAS TIME, ON FEBRUARY 1, 2004

         THIS CERTIFIES that, for value received,

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

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

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

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

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

<PAGE>   2

Class "Y" Warrant No.
Page 2

fraction of a share of Common Stock. In lieu of issuing a fraction of a share
remaining after exercise of this Warrant as to all full shares covered hereby,
the Corporation shall either (1) pay therefor cash equal to the same fraction of
the then current Warrant purchase price per share or, at its option, (2) issue
scrip for the fraction, in registered or bearer form approved by the board of
directors of the Corporation, which shall entitle the holder to receive a
certificate for a full share of Common Stock on surrender of scrip aggregating a
full share. Scrip may become void after a reasonable period (but not less than
six months after the expiration date of this Warrant) determined by the board of
directors and specified in the scrip. In case of the exercise of this Warrant
for less than all the shares purchasable, the Corporation shall cancel the
Warrant and execute and deliver a new Warrant of like tenor and date for the
balance of the shares purchasable.

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

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

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

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

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

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

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

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

         (2) the Warrant purchase price in effect, and the number of shares
purchasable under this Warrant, immediately prior to the date upon which the
change becomes effective, shall be proportionately adjusted (the price to the
nearest cent). Irrespective of any adjustment or change in the Warrant purchase
price or the number of shares purchasable under this or any other Warrant of
like tenor, the Warrants theretofore and thereafter issued may continue to
express the Warrant purchase
<PAGE>   3

Class "Y" Warrant No.
Page 3

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

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

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

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

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

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

<PAGE>   4
Class "Y" Warrant No.
Page 4

         Witness the seal of the Corporation and the signatures of its
authorized officers.

Date______________________(Seal)             PROBEX CORP.

ATTEST:

-----------------------------------          -----------------------------------
Thomas G. Plaskett                           Bruce A. Hall
Chief Executive Officer & President          Chief Financial Officer & Secretary

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Class "Y" Warrant No.
Page 5

                                  TRANSFER FORM

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

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

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

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

Date:

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

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

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

In the presence of              Signature guaranteed by

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

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Class "Y" Warrant No.
Page 6

                                  EXERCISE FORM

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

Date:

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

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

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

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

                                Taxpayer ID No.
                                                --------------------------------<PAGE>   1
 Confidential Treatment Requested. Confidential Portions of this document have
       been redacted and have been separately filed with the Commission.

                                                                   EXHIBIT 10.18

                           MEMORANDUM OF UNDERSTANDING

This MEMORANDUM OF UNDERSTANDING is entered into effective as of January 1, 2000
by and between PROBEX CORP. ("Probex") and BECHTEL CORPORATION ("Bechtel").

WHEREAS, Probex has developed ProTerra(TM), a proprietary process for
manufacturing premium base lubricating oil from used oil, and Bechtel's
proprietary MP Refining(SM) technology is a good complement to the finishing
stage of ProTerra(TM); and

WHEREAS, to capitalize on their respective complementary resources and
capabilities, Probex wishes to obtain Bechtel's assistance in the development,
financing, engineering, design, procurement, construction, and operation
worldwide of used oil re-refining facilities based on ProTerra(TM) and enhanced
by MP Refining(SM); and

WHEREAS, to that end Probex and Bechtel have effective as of the date hereof
entered into master agreements under which Bechtel shall license the MP
Refining(SM) process to Probex and perform process engineering and other
front-end engineering services for Probex;

NOW, THEREFORE, for the mutual promises and consideration contained herein,
Probex and Bechtel hereby further agree as follows:

1. Designated Engineer/Constructor: Probex and Bechtel shall in good faith use
their best efforts to complete and execute contractual arrangements whereby
Bechtel is designated Probex's engineer constructor for all Probex facilities
worldwide for which Probex has the right to designate an engineer constructor

2. Turnkey Engineering, Procurement and Construction Contract: Probex and
Bechtel shall in good faith use their best efforts to complete and execute by
[Confidential material redacted and filed separately with the Commission.] a
master turnkey EPC contract and the contract release for the first Probex
facility with performance guarantees and credit support elements that are
consistent with and incorporate the business points contained in the term sheet
that is Attachment A hereto.

3. Operations and Maintenance Agreement: Bechtel shall inform Probex by April,
2000 whether Bechtel intends to enter into good faith negotiations on a mutually
satisfactory master operations and maintenance agreement for the first Probex
facility, and for subsequent facilities as appropriate.

4. Marketing Assistance: Bechtel will provide marketing assistance to Probex in
identifying and developing opportunities for commercial application of
ProTerra(TM). Compensation for marketing assistance by Bechtel will be included
in the pricing provisions of the master EPC agreement.

5. Press Release: Probex and Bechtel shall jointly issue immediately upon the
execution of this Memorandum of Understanding the press release which is
Attachment

                                       1
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B hereto. Bechtel will have the right to timely review and approve any press
release which mentions Bechtel.

6. Termination: This Memorandum of Understanding shall terminate and be of no
further force should the parties not be able to reach agreement on EPC contracts
by [Confidential material redacted and filed separately with the Commission.]
unless the parties extend this target date by mutual agreement.

7. Disclosures: In the event Probex is required to disclose this MOU, contracts,
or any work products to the SEC, Probex and Bechtel will consult and agree in
advance on which sections will be redacted and filed separately with the SEC.

It is agreed that any work product prepared by Bechtel shall not be disclosed in
connection with any public securities offering without Bechtel's prior written
consent. Any such work product shall only be disclosed to sophisticated
investors with prior notification to Bechtel and with an appropriate disclaimer
putting such investors on notice of the requirement to perform their own due
diligence prior to making any investment. Extracts of such work product which
attribute the extracted information to Bechtel will only be disclosed to third
parties after prior notification to Bechtel and after these third parties have
entered into appropriate confidentiality agreements with Probex and a
contractual relationship with Probex pursuant to which such third parties are
required to have access to such excerpts in connection with the performance of
their duties to Probex. Otherwise, such extracts of such work product will not
be disclosed to third parties without Bechtel's prior review.

Work product is defined as all information and documents produced by Bechtel
pursuant to its contractual obligations to Probex.

IN WITNESS WHEREOF, Probex and Bechtel have entered into this Memorandum of
Understanding effective as of the date first set forth hereinabove.

PROBEX CORP.                                BECHTEL CORPORATION

By: /s/ THOMAS G. PLASKETT                  By: /s/ THOMAS NARDI
   --------------------------                  ---------------------------------
         Thomas G. Plaskett                          Thomas Nardi
         Chairman and CEO                            Principal Vice President

                                       2
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                                                                    Attachment A

                 Probex Corp. Lube Oil Manufacturing Initiative

                    MASTER TURNKEY ENGINEERING, PROCUREMENT,
                CONSTRUCTION, STARTUP AND COMMISSIONING CONTRACT

                                   Term Sheet

1. The Contract shall apply to all Probex Corp. used lubricating oil re-refining
facilities worldwide for which Probex or an affiliated or subsidiary entity has
the right to designate the engineer/constructor ("the Probex Facilities"). One
master EPC contract will be prepared giving general terms and conditions and
formulas for compensation. Individual facilities will be contracted through
numbered releases to the master contract which describe the site specific scope,
compensation, and deviations from the master contract terms and conditions.

2. The definitive form and content of the master contract shall facilitate
Probex's ability to secure non-recourse debt and/or other financing for the
Probex Facilities, and the master contract and its first release shall contain
such terms and conditions as are reasonable, appropriate, and customary in that
context. If necessary for credit support purposes, Bechtel will enter into
individual EPC Contracts for each Probex Facility with Probex or one of Probex's
affiliates.

3. The Probex Facilities shall be based upon ProTerra(TM), Probex's proprietary
technology, which has discrete pretreatment, distillation and finishing stages,
as complemented by Bechtel Corporation's proprietary MP Refining(SM) solvent
extraction finishing process where applicable.

4. Bechtel's services shall include but not be limited to the design,
engineering, procurement, construction, commissioning, start up, and performance
testing of the Probex Facilities (all of which in totality shall be referred to
hereinafter as "the Services"), commencing with a facility or facilities to be
designated by Probex. The Services shall include any and all engineering and
other technical and ancillary services performed under any preceding contracts
by Bechtel for Probex directly or indirectly for each Probex Facility.

5. To the maximum extent feasible commensurate with the degree of steady work
load on Probex facilities, Bechtel shall manage the resources, including
personnel, that it dedicates to the performance of the Services on a
programmatic basis to maximize the efficiencies and cost savings to Probex
associated with a multi-facility program. [Confidential material redacted and
filed separately with the Commission.]

                                       1
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6. Bechtel shall perform the Services for each Facility in accordance with
detailed design criteria, specifications, and engineering drawings defining the
physical scope and required performance characteristics of each Facility,
including but not limited to electrical, hydraulic, and mechanical systems and
utilities, as prepared by Bechtel and approved by Probex.

7. The nature and scope of Bechtel's startup services shall be mutually agreed
to by Probex and Bechtel.

8. Approved lists of major equipment vendors and subcontractors will be included
in the Master EPC contract. The approved lists of vendors and subcontractors can
be modified by mutual consent of Probex and Bechtel, as appropriate, in each
contract release.

9. Bechtel may be authorized to purchase as Probex's agent tangible equipment
and material for incorporation into the Facility if necessary and appropriate to
avoid double taxation. [Confidential material redacted and filed separately with
the Commission.]

10. Probex shall pay Bechtel a lump sum turnkey price (or, if the parties agree,
a not-to-exceed price) for the performance of the Services associated with each
Facility, which fixed price will be determined by open-book discussions for
estimating costs. Payment of the fixed price shall be made in installments in
concert with Bechtel's progress in performing the Services and expenses incurred
associated with each Facility. Such fixed price for each Facility shall only be
adjusted in response to changes in the scope of the Services and/or the Facility
ordered by Probex, for changed conditions from those described in the scoping
documents included in a contract release, or for force majeure events as agreed
between the parties.

11. Probex, HSB, and Probex's lenders and their representatives, including
potentially a consulting engineer, shall have reasonable access to Bechtel's
engineering facilities and each Facility site for the purpose of inspecting and
monitoring Bechtel's performance of the Services associated with each Facility
and the multi-plant program as a whole.

12. Probex and Bechtel shall each be responsible for securing and paying for
licenses and permits associated with their respective roles and
responsibilities.

13. Probex shall provide, arrange for, or provide Bechtel access to the
necessary utilities, including electrical energy, and sufficient used oil
feedstock for the commissioning and startup of each Probex Facility.

14. Bechtel shall conduct the performance testing of such facility in
conjunction with Probex in accordance with agreed upon test criteria, procedures
and duration.

                                       2
<PAGE>   5
15. Bechtel shall guarantee to Probex the Date of Mechanical Completion of each
Probex Facility, which dates shall be adjusted, if at all, only in accordance
with agreed-upon industry standard practices such as changes requested by
Probex, changed conditions, and/or force majeure events. The definition of
Mechanical Completion shall be included in the master EPC contract. In the event
that Bechtel fails to achieve Mechanical Completion of a Facility by the
agreed-upon date, Bechtel shall pay to Probex liquidated damages, the
calculation of which will be based upon a formula to be mutually agreed to by
Probex and Bechtel, and included in the master EPC contract (unless explicitly
superceded in the associated contract release). Such liquidated damages shall be
Probex's exclusive remedy for delay and are intended to be at a level sufficient
to meet lender requirements.

16. Bechtel shall guarantee its performance of the Services (as covered in any
Technical Services or EPC contracts) in accordance with accepted professional
engineering, procurement, and construction standards, and therefore guarantee
the physical, mechanical, and structural performance of each Probex Facility.
Bechtel shall correct at its cost any deficiencies in the Services for each
Probex Facility upon notice from Probex within an agreed-to warranty period,
subject to a total liability cap to be included in the master EPC contract and
the associated contract release.

17. Bechtel shall guarantee to Probex that the MP Refining Unit portion of each
Facility shall perform in accordance with agreed-to Performance Standards as
confirmed by the performance testing referenced above. In the event that such MP
Refining(SM) Unit fails to meet the Performance Standards by an agreed-upon
date, Bechtel shall pay to Probex liquidated damages, the calculation of which
will be based upon a formula to be mutually agreed to by Probex and Bechtel, and
included in the Master EPC Contract (unless explicitly superceded in the
associated contract release). Such liquidated damages shall be Probex's
exclusive remedy for performance shortfall and are intended to be at a level
sufficient to meet lender requirements.

18. The terms and conditions of the Master EPC Contract and contract releases,
and in particular those associated directly and indirectly with the performance
of the initial Probex Facilities, are intended to be [Confidential material
redacted and filed separately with the Commission.] complementary to the HSB
system performance insurance ("SPI") being provided to support the project
financing of at least the initial Probex Facilities, such that the Contract and
the SPI provide Probex's lenders with sufficient security and protection
regarding the performance of at least those initial Probex facilities.

19. If and when appropriate, following the successful financing, installation
and operation of the initial Probex Facilities, in place of the HSB SPI
referenced in Section 18, above, and the MP Refining performance guarantee as
specified in Section 17, above, Bechtel will consider providing performance
guarantees for the totality of the ProTerra/MP Refining process as appropriate
and necessary to support the project financing of subsequent Probex Facilities.

                                       3
<PAGE>   6

20. The final acceptance of each Probex Facility by Probex and HSB shall occur
following Bechtel's completion of all punch list items for each such Probex
Facility.

21. Except in the case of willful misconduct, Bechtel's total liability to
Probex for all causes, except for the re-performance of deficient engineering
services, shall be limited to a mutually agreed to maximum total liability cap .
Schedule and performance liquidated damages and all warranty work other than
re-performance of deficient engineering, will be sub-capped under the total
liability cap in amounts to be mutually agreed. Other than schedule and
performance liquidated damages and any specific indemnities negotiated and
agreed to by both parties, each party shall release the other, its
subcontractors and suppliers from liability for consequential damages, howsoever
arising, and whether in contract, tort or otherwise.

22. Probex and its insurance broker and Bechtel shall agree upon insurance
arrangements and coverages, and other risk management devices, for the
multi-plant program as a whole and for each Facility that support the project
financing of those Facilities. If Bechtel is required to assume risk of loss
during construction then Bechtel will furnish appropriate Builders Risk
insurance.

23. Probex and Bechtel shall be bound by appropriate bi-lateral confidentiality
obligations with regard to the existence of the Contract, the progress that the
parties are making thereunder, and specific confidential information transferred
from each party to the other.

24. The ownership of work product shall be as outlined in the Solvent Finishing
Unit Technical Services Agreement and the Wellsville Plant Process Engineering
and Technical Services Agreement to be signed contemporaneously with the
execution of the EPC MOU.

                                       4

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