<PAGE>

                                                                   EXHIBIT 10.48

                                PLEDGE AGREEMENT
                                     (Note)

         THIS PLEDGE AGREEMENT (this "Agreement") is made this 31st day of
December 2000, by and between Bruce A. Hall ("Pledgor"), and Probex Corp.
("Secured Party").

                                    RECITALS:

         A. Bruce A. Hall ("Debtor") has executed that certain Promissory Note,
dated December 31, in the original principal amount of $100,000 in favor of
Secured Party (the "Note");

         B. Pledgor is the owner of certain Securities (as defined below) in
Debtor and expects to receive substantial direct and indirect benefits from the
loans made to Debtor pursuant to the Note; and

         C. As security for the payment and performance of all of Debtor's
obligations pursuant to the Note, Pledgor has agreed to grant Secured Party a
Security Interest (as defined below) in the Collateral (as defined below).

                                   AGREEMENTS:

         In consideration of the premises, the covenants and agreements
contained herein, and other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, Secured Party and Pledgor do hereby
agree as follows:

         1. Definitions. The following terms shall have the meanings indicated
below and shall be construed to have the broadest possible meanings permitted
under the Code:

                  "Code" means the Uniform Commercial Code as enacted by the
State of Texas, as it shall be amended from time to time.

                  "Collateral" means the Securities of Debtor owned by Pledgor
listed on Schedule 1 hereto, and the certificates representing such Securities,
together with all additions, replacements, substitutions, increases, profits,
proceeds, dividends, distributions and products thereof, in any form and
wherever located.

                  "Event of Default" and "Default" means (i) an "Event of
Default" (as defined in the Note), or (ii) the breach by Pledgor of its
obligations hereunder.

                  "Securities" means any corporate stock (including stock of
closely held corporations), partnership interest or limited liability company
interest, any warrants or rights to acquire a security, and in addition,
includes all property included in the definition of "security" as used in the
Code.

                  "Security Interest" means the security interest (as that term
is defined by the Code) granted by this Agreement.



<PAGE>

         2. Grant of Security Interest. Pledgor hereby delivers to the Secured
Party certificates evidencing, and grants to the Secured Party a continuing and
unconditional Security Interest in, the Collateral, accompanied by stock powers
in substantially the form of Exhibit A attached hereto and made a part hereof
(the "Powers"), duly executed in blank, to secure the prompt, timely and
complete payment of all obligations and liabilities of Debtor to the Secured
Party now existing or hereafter arising under the Note and the full, complete
and timely performance of any and all existing or future obligations of such
Debtor under the Note. All such present and future obligations under the Note
are referred to herein as the "Secured Obligations."

         3. Representations and Warranties. The Pledgor represents and warrants
as follows:

                  (a) The Pledgor is the sole legal and beneficial owner of the
Collateral, free and clear of all claims, pledges, liens, encumbrances, charges
and security interests of every nature whatsoever, except for the security
interest created by this Agreement;

                  (b) The Pledgor has the capacity, power and authority to enter
into this Agreement;

                  (c) Except for the restrictions imposed by applicable federal
or state securities laws, there are no restrictions upon the voting rights
associated with the Collateral or upon the transfer of any of the Collateral;
and

                  (d) The pledge of the Collateral pursuant to this Agreement
creates a valid and first priority security interest in the Collateral, in favor
of the Secured Party, securing the payment and performance of the Secured
Obligations.

         4. Covenants of Pledgor. So long as this Agreement has not been
terminated as provided hereafter, Pledgor:

                  4.1 Title. Will defend the Collateral against the claim of all
other persons;

                  4.2 No Encumbrances. Will keep the Collateral free of all
security interests, voting trust agreements, or other interests and
encumbrances, except the Security Interest;

                  4.3 No Sale, Etc. Will not assign, deliver, sell, transfer,
lease or otherwise dispose of (including dispositions by operation of law) any
portion of the Collateral, or any interest therein without the prior written
consent of Secured Party;

                  4.4 Financing Statements. Will execute and deliver to Secured
Party such stock powers, financing statements, certificates and other documents
and instruments, pay all costs including costs of filing financing statements
and other documents in any public offices requested by Secured Party and take
such other action as Secured Party may deem advisable to perfect the Security
Interest created by this Agreement;

                  4.5 Taxes. Will pay all taxes (including documentary stamp
taxes and intangible taxes), assessments and other charges of every nature which
may be levied or assessed



                                       2
<PAGE>

against the Collateral, or imposed upon Pledgor or Secured Party by reason of
this Agreement; and

                  4.6 Cooperation. Will take other action reasonably requested
by Secured Party to carry out the terms of this Agreement, to preserve the
Collateral, and to preserve and perfect the Security Interest of Secured Party.

         5. Default. If an Event of Default shall occur and be continuing, the
Secured Party may take all of the actions or remedies specified in Section 6
hereof ("Remedies") or elsewhere herein.

         6. Remedies.

                  6.1 If an Event of Default shall have occurred and be
continuing, the Secured Party shall have all rights and remedies of a secured
party under the Code and such other rights and remedies as may be available
hereunder, under other applicable law or pursuant to contract. Pledgor agrees
that any notice by Secured Party of the sale or disposition of the Collateral or
any other intended section hereunder, whether required by the Code or otherwise,
shall constitute reasonable notice to Pledgor if the notice is mailed to Pledgor
by regular or certified mail, postage prepaid, at least ten (10) days before the
action to be taken. During such ten (10) day period, Pledgor shall have the
right to cure any defaults by paying to Secured Party the amount of the Secured
Obligations and any other obligations secured hereby. Pledgor also agrees to pay
all costs and expenses incurred by the Secured Party in enforcing this Agreement
and realizing upon any Collateral (including reasonable attorneys' fees whether
or not suit is brought and whether or not incurred in connection with trial,
appeals or insolvency action).

                  6.2 Pledgor agrees that in any sale of any Collateral, Secured
Party is hereby authorized to comply with any limitation or restriction in
connection with such sale as it may be advised by counsel is necessary in order
to avoid any violation of applicable law (including, without limitation,
compliance with such procedures as may restrict the number of prospective
bidders and purchasers of Securities, require that such prospective bidders and
purchasers have certain qualifications, and restrict such prospective bidders
and purchasers to persons who will represent and agree that they are purchasing
for their own account for investment and not with a view to the distribution or
resale of such Collateral, or in order to obtain any required approval of the
sale or of the purchaser by any governmental regulatory authority or official)
and Pledgor further agrees that such compliance shall not result in such sale
being considered or deemed not to have been made in a commercially reasonable
manner, nor shall the Secured Party be liable nor accountable to Pledgor for any
discount allowed by reason of the fact that such Collateral is sold in
compliance with any such limitation or restriction. Pledgor further agrees that
any sales by the Secured Party shall not be considered to be other than "public
sales" within the meaning of Section 9.504 of the Uniform Commercial Code
because such sales or solicitations are structured to comply with such
limitations or restrictions, the intent of the parties being that any public
sale be subject to such limitations and restrictions.

         7. Voting of Pledged Shares. Pledgor hereby irrevocably constitutes and
appoints Secured Party in connection with all Securities which comprise the
Collateral, whether or not the Securities have been transferred into the nature
of Secured Party or its nominee, as Pledgor's



                                       3
<PAGE>

proxy (and such proxy shall be deemed to be coupled with an interest) with full
power, solely upon the occurrence and during the continuance of an Event of
Default and the exercise of Secured Party's rights under this Section 7, to:

                  (a) attend all meetings of Securities holders of Debtor held
after the date of this Agreement and to vote the Securities at those meetings in
such manner as Secured Party shall in its sole discretion deem appropriate,
including without limitation, in favor of liquidation of Debtor;

                  (b) to consent in the sole discretion of Secured Party to any
action by or concerning Debtor for which the consent of the Securities holders
of Debtor is or may be necessary or appropriate; and

                  (c) without limitation to do all things which Pledgor could do
as a Security holder of Debtor, giving to Secured Party full power of
substitution and revocation.

The proxy contained in this paragraph shall terminate when this Agreement
terminates as provided hereafter. Pledgor hereby agrees not to give or permit to
exist any other proxies in derogation of this proxy so long as this Agreement is
in force.

         8. Transfer Securities of Record. Pledgor authorizes and appoints
Secured Party, effective upon occurrence of a Default, as Pledgor's
attorney-in-fact to transfer all or any part of the Securities which comprise
any part of the Collateral into Secured Party's name or that of its nominee so
that Secured Party or its nominee may appear of record as the sole owner of the
Securities. After the occurrence and during the continuance of any Default,
Pledgor waives all rights to be advised or to receive any notices, statements or
communications received by Secured Party or its nominee as such record owner.

         9. Distributions In Respect of Collateral.

                  9.1 Upon the occurrence and during the continuance of an Event
of Default and the exercise by Secured Party of its rights under this Section 9,
Pledgor assigns to, and authorizes Secured Party to receive, any interest,
principal, dividends, distributions, or other income or payments of whatever
nature (whether in cash or in kind) now or hereafter made in respect of the
Collateral, including those made in connection with the dissolution,
liquidation, sale of assets, merger, consolidation, or other reorganization of
Debtor, or any stock dividend, stock split, recapitalization, reclassification
or otherwise (collectively, "Distributions"), to surrender such Collateral or
any part thereof in exchange therefor, and to hold any such Distribution as part
of the Collateral.

                  9.2 After the occurrence and during the continuance of an
Event of Default, Pledgor will not demand or receive any income or Distribution
with respect to the Collateral and if Pledgor receives any such Distributions,
Pledgor will hold such Distributions in trust and deliver them promptly in the
form received to Secured Party to hold as Collateral. After the occurrence and
during the continuance of an Event of Default, Secured Party may apply any net
cash Distributions to payment of any of the Secured Obligations, but Secured
Party shall account for and pay over to Pledgor any Distributions remaining
after full payment of such obligations.



                                       4
<PAGE>

         10. Miscellaneous Provisions.

                  10.1 Perfection. Pledgor authorizes Secured Party at Pledgor's
expense to file any financing statements relating to the Collateral (without
Pledgor's signature thereon) which Secured Party deems appropriate and Pledgor
appoints Secured Party as Pledgor's attorney-in-fact to execute any such
financing statements in Pledgor's name and to perfect and to continue perfection
of the Security Interest.

                  10.2 Right to Perform Obligations. Upon Pledgor's failure to
perform any of its duties hereunder and after five (5) days written notice of
such failure from Secured Party, Secured Party may, but it shall not be
obligated to, perform any of such duties and Pledgor shall forthwith upon demand
reimburse Secured Party for any expenses incurred by Secured Party in so doing;
provided that no notice shall be required if in Secured Party's reasonable
judgment such delay would materially jeopardize or impair the value of the
Collateral.

                  10.3 No Waiver. No delay or omission by Secured Party in
exercising any right hereunder shall operate as a waiver of that or any other
right, and no single or partial exercise of any right shall preclude Secured
Party from any other or further exercise of the right or the exercise of any
other right or remedy. All rights and remedies of Secured Party under this
Agreement and under the Code shall be deemed cumulative.

                  10.4 Care of Collateral, Etc. Secured Party shall exercise
reasonable care in the custody and preservation of the Collateral to the extent
required by law and it shall be deemed to have exercised reasonable care if it
takes such action for that purpose as Pledgor shall reasonably request in
writing; provided, however, no omission to do any act not requested by such
Pledgor shall be deemed a failure to exercise reasonable care and no omission to
comply with any requests by such Pledgor shall of itself be deemed a failure to
exercise reasonable care.

                  10.5 Enforcement. If an Event of Default shall occur, Secured
Party may demand, collect and sue for all amounts owed pursuant to the
Collateral or for proceeds of any Collateral (either in Pledgor's name or
Secured Party's name at the latter's option), with the right to enforce,
compromise, settle or discharge any such amounts. After Default, Pledgor
appoints Secured Party as such Pledgor's attorney-in-fact to endorse such
Pledgor's name on all checks, commercial paper and other document or instruments
pertaining to Collateral or proceeds.

                  10.6 Other Rights. Pledgor acknowledges that its obligations
hereunder are absolute and unconditional and authorizes Secured Party without
affecting Pledgor's obligations hereunder from time to time to take the
following actions, whether or not increasing the risk of loss to Pledgor:

                  (a) to take from any party and hold collateral (other than the
Collateral) for the payment of the Secured Obligations or any party thereof, and
to exchange, enforce or release such collateral or any guaranty of payment of
the Secured Obligations or any part thereof and to release or substitute any
such endorser or guarantor or any party who has given any Security Interest in
any collateral as security for the payment of the Secured Obligations or any
party thereof or any party in any way obligated to pay the Secured Obligations
or any part thereof; and



                                       5
<PAGE>

                  (b) upon the occurrence of an Event of Default to direct the
manner of the disposition of the Collateral and any other collateral and the
enforcement of any endorsements or guaranties relating to the Secured
Obligations or any party thereof as Secured Party in its sole discretion may
determine, consistent with the provisions of Section 6.

                  10.7 Successors and Assigns. This Agreement shall be binding
upon and inure to the benefit of Pledgor and Secured Party and their respective
successors and assigns, except that Pledgor may not assign any of its rights or
obligations under this Agreement without the prior written consent of Secured
Party.

                  10.8 Benefit. The terms "Secured Party" and "Pledgor" as used
in this Agreement include the heirs, personal representatives and successors or
assigns of those parties and this Agreement shall benefit and bind such parties.
If more than one person is named herein as Pledgor, the obligation hereunder
shall be joint and several, subject to the nonrecourse provisions set forth
herein.

                  10.9 Amendment. This Agreement may not be modified or amended
nor shall any provision of it be waived except in writing signed by Pledgor and
by an authorized officer of Secured Party.

                  10.10 Governing Law; Venue. This Agreement shall be governed
by and construed under the Uniform Commercial Code and any other applicable laws
of the State of Texas in effect from time to time. ANY ACTION RELATED TO AND/OR
BASED UPON THE SUBJECT MATTER OF THIS AGREEMENT SHALL BE BROUGHT IN THE COURT OF
PROPER JURISDICTION IN DALLAS COUNTY, TEXAS.

                  10.11 Term. This Agreement shall remain in force until the
full satisfaction and discharge of the Note. Upon termination of the Agreement,
Secured Party shall take all steps reasonably requested (but at Pledgor's cost)
by Pledgor to release its Security Interest and Pledgor shall be discharged in
full from any and all obligations under this Agreement.

                  10.12 Notices. Notice required or permitted to be given
hereunder shall be given to the parties at the addresses set forth on the
signature pages of this document or at such other address as may be designated
in writing from time to time by one party to the other. Any such notices or
communications shall be deemed to be received upon the earlier of actual receipt
at the address provided or, if mailed, five (5) business days after mailing by
first class mail.

                  10.13 Powers. All powers, rights, proxies and privileges
granted to Secured Party herein are coupled with an interest and are
irrevocable.

                  10.14 Counterparts. This Agreement may be executed in any
number of counterparts and by different parties thereto in separate
counterparts, each of which when so executed and delivered shall be deemed as
original and all of which were taken together shall constitute but one and the
same instrument.

                         [Signatures on Following Page]



                                       6
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed this instrument as
of the date first stated above.



                                       PLEDGOR

                                       Bruce A. Hall

                                       By:   /s/ Bruce Hall
                                             -----------------------------------
                                       Name: Bruce Hall
                                       Its:
                                             -----------------------------------

                                       Address: 836 Blue Jay Lane
                                                Coppell, TX 75019

                                       SECURED PARTY:

                                       Probex Corp.



                                       By:   /s/ Charles Rampacek
                                             -----------------------------------
                                       Name: Charles Rampacek
                                       Its:  Chairman, CEO & President

                                       Address: 13355 Noel Road, Suite 1200
                                                Dallas, TX 75240



                                       7
<PAGE>

                                    EXHIBIT A

                             IRREVOCABLE STOCK POWER

         Bruce A. Hall hereby irrevocably appoints, with full power of
substitution, an officer of Probex Corp. to transfer on the books of Transfer
Online, shares of Common Stock of Probex Corp., now standing in the name of
Bruce A. Hall, represented by Common Stock Purchase Warrants in the amount of
120,941 shares of an exercise price of $1.00 per share dated June 4, 1999,
expiring June 4, 2001 and 27,294 shares at an exercise price of $0.55 per share
dated June 4, 1999, expiring June 4, 2004.

Dated: 12/31/00



                                       By:    /s/ Bruce Hall
                                              ----------------------------------
                                       Title:
                                              ----------------------------------



<PAGE>

                                   SCHEDULE 1

                                   COLLATERAL



o       Bruce A. Hall      -   120,941 $1.00 warrants
o       Bruce A. Hall      -   27,294 $0.55 warrants
o       Bruce A. Hall      -   All Stock Options