Document:

<PAGE>
                                                                   EXHIBIT 10(a)

                       SEVENTH AMENDMENT TO LOAN AGREEMENT

         THIS SEVENTH AMENDMENT TO LOAN AGREEMENT (this "Amendment"), dated as
of August 31, 2002, is between SOUTH HAMPTON REFINING CO., a Texas corporation
("Borrower'), and SOUTHWEST BANK OF TEXAS, N.A., a national banking association
("Lender").

                                    RECITALS:

         A. Borrower and Lender entered into that certain Loan Agreement dated
as of September 30, 1999, as amended by First Amendment to Loan Agreement dated
as of June 20, 2000, Second Amendment to Loan Agreement dated as of May 31,
2001, Third Amendment to Loan Agreement dated as of July 31, 2001, Fourth
Amendment to Loan Agreement dated as of October 31, 2001, Fifth Amendment to
Loan Agreement dated as of December 31, 2001 and Sixth Amendment to Loan
Agreement dated as of April 30, 2002 (the "Agreement").

         B. Pursuant to the Agreement, Texas Oil & Chemical Co. II, Inc., a
Texas corporation ("Guarantor") executed that certain Guaranty Agreement dated
as of June 20,2000 (the "Guaranty") pursuant to which Guarantor guaranteed to
Lender the payment and performance of the Obligations (as defined in the
Agreement).

         C. Borrower and Lender now desire to amend the Agreement as herein set
forth.

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

                                   ARTICLE I.

                                   Definitions

         Section 1.1. Definitions. Capitalized terms used in this Amendment, to
the extent not otherwise defined herein, shall have the meanings given to such
terms in the Agreement, as amended hereby.

<PAGE>

                                   ARTICLE II.

                                   Amendments

         Section 2.1. Amendment to Certain Definitions. The definition of the
term "Termination Date" contained in Section 1.1 of the Agreement is amended to
read in its entirety as follows:

                  "Termination Date" means 11:00 a.m., Houston, Texas time on
         December 31, 2002, or such earlier date on which the Commitment
         terminates as provided in this Agreement.

         Section 2.2. Amendment to Exhibits. Exhibit "A" (Note) to the Agreement
is amended to conform in its entirety to Annex "A" to this Amendment.

                                  ARTICLE III.

                              Conditions Precedent

         Section 3.1. Conditions. The effectiveness of this Amendment is subject
to the receipt by Lender of the following in form and substance satisfactory to
Lender:

                  (a) Certificate - Borrower. A certificate of the Secretary or
         another officer of Borrower acceptable to Lender certifying (i)
         resolutions of the board of directors of Borrower which authorize the
         execution, delivery and performance by Borrower of this Amendment and
         the other Loan Documents to which Borrower is or is to be a party and
         (ii) the names of the officers of Borrower authorized to sign this
         Amendment and each of the other Loan Documents to which Borrower is or
         is to be a party together with specimen signatures of such officers.

                  (b) Certificates of Existence and Good Standing - Borrower.
         Certificates of the appropriate governmental officials regarding the
         existence and good standing of Borrower in the state of Texas.

                  (c) Note. The Note executed by Borrower.

                  (d) Additional Information. Such additional documents,
         instruments and information as Lender may request.

         Section 3.2. Additional Conditions. The effectiveness of this Amendment
is also subject to the satisfaction of the additional conditions precedent that
(a) the representations and warranties contained herein and in all other Loan
Documents, as amended hereby, shall

                                      -2-

<PAGE>

be true and correct as of the date hereof as if made on the date hereof, (b) all
proceedings, corporate or otherwise, taken in connection with the transactions
contemplated by this Amendment and all documents, instruments and other legal
matters incident thereto shall be satisfactory to Lender, and (c) no Event of
Default or Unmatured Event of Default shall have occurred and be continuing.

                                   ARTICLE IV.

                 Ratifications, Representations, and Warranties

         Section 4.1. Ratifications. The terms and provisions set forth in this
Amendment shall modify and supersede all inconsistent terms and provisions set
forth in the Agreement and except as expressly modified and superseded by this
Amendment, the terms and provisions of the Agreement are ratified and confirmed
and shall continue in full force and effect. Borrower and Lender agree that the
Agreement as amended hereby shall continue to be the legal, valid and binding
obligation of such Persons enforceable against such Persons in accordance with
its terms.

         Section 4.2. Representations, Warranties and Agreements. Borrower
hereby represents and warrants to Lender that (a) the execution, delivery, and
performance of this Amendment and any and all other Loan Documents executed or
delivered in connection herewith have been authorized by all requisite action on
the part of Borrower and will not violate the articles of incorporation or
bylaws of Borrower, (b) the representations and warranties contained in the
Agreement as amended hereby, and all other Loan Documents are true and correct
on and as of the date hereof as though made on and as of the date hereof, (c) no
Event of Default or Unmatured Event of Default has occurred and is continuing,
(d) Borrower is in full compliance with all covenants and agreements contained
in the Agreement as amended hereby, (e) Borrower is indebted to Lender pursuant
to the terms of the Note, as the same may have been renewed, modified, extended
and rearranged, including, without limitation, renewals, modifications and
extensions made pursuant to this Amendment, (f) the liens, security interests,
encumbrances and assignments created and evidenced by the Loan Documents are,
respectively, valid and subsisting liens, security interests, encumbrances and
assignments and secure the Note as the same may have been renewed, modified or
rearranged, including, without limitation, renewals, modifications and
extensions made pursuant to this Amendment, and (g) Borrower has no claims,
credits, offsets, defenses or counterclaims arising from the Loan Documents or
Lender's performance under the Loan Documents.

                                      -3-

<PAGE>

                                   ARTICLE V.

                                  Miscellaneous

         Section 5.1. Survival of Representations and Warranties. All
representations and warranties made in this Amendment or any other Loan
Documents including any Loan Document furnished in connection with this
Amendment shall fully survive the execution and delivery of this Amendment and
the other Loan Documents, and no investigation by Lender or any closing shall
affect the representations and warranties or the right of Lender to rely on
them.

         Section 5.2. Reference to Agreement. Each of the Loan Documents,
including the Agreement and any and all other agreements, documents, or
instruments now or hereafter executed and delivered pursuant to the terms hereof
or pursuant to the terms of the Agreement, as amended hereby, are hereby amended
so that any reference in such Loan Documents to the Agreement shall mean a
reference to the Agreement, as amended hereby.

         Section 5.3. Expenses of Lender. As provided in the Agreement, Borrower
agrees to pay on demand all costs and expenses incurred by Lender in connection
with the preparation, negotiation and execution of this Amendment and the other
documents and instruments executed pursuant hereto and any and all amendments,
modifications and supplements thereto, including, without limitation, the costs
and fees of Lender's legal counsel, and all costs and expenses incurred by
Lender in connection with the enforcement or preservation of any rights under
the Agreement, as amended hereby, or any other Loan Document, including, without
limitation, the costs and fees of Lender's legal counsel.

         Section 5.4. Severability. Any provision of this Amendment held by a
court of competent jurisdiction to be invalid or unenforceable shall not impair
or invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

         Section 5.5. APPLICABLE LAW. THIS AMENDMENT AND ALL OTHER LOAN
DOCUMENTS EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE
PERFORMABLE IN HOUSTON, HARRIS COUNTY, TEXAS AND SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS.

         Section 5.6. Successors and Assigns. This Amendment is binding upon and
shall inure to the benefit of Lender and Borrower and their respective
successors and assigns, except Borrower may not assign or transfer any of its
rights or obligations hereunder without the prior written consent of Lender.

                                      -4-

<PAGE>

         Section 5.7. Counterparts. This Amendment may be executed in one or
more counterparts, each of which when so executed shall be deemed to be an
original, but all of which when taken together shall constitute one and the same
instrument.

         Section 5.8. Effect of Waiver. No consent or waiver, express or
implied, by Lender to or for any breach of or deviation from any covenant,
condition or duty by Borrower shall be deemed a consent or waiver to or of any
other breach of the same or any other covenant, condition or duty.

         Section 5.9. Headings. The headings, captions, and arrangements used in
this Amendment are for convenience only and shall not affect the interpretation
of this Amendment.

         SECTION 5.10. ENTIRE AGREEMENT. THIS AMENDMENT AND ALL OTHER
INSTRUMENTS, DOCUMENTS, AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS AMENDMENT EMBODY THE FINAL, ENTIRE AGREEMENT AMONG THE PARTIES HERETO WITH
RESPECT TO THE SUBJECT MATTER HEREOF AND THEREOF AND SUPERSEDE ANY AND ALL PRIOR
COMMITMENTS, AGREEMENTS, REPRESENTATIONS AND UNDERSTANDINGS, WHETHER WRITTEN OR
ORAL, RELATING TO THIS AMENDMENT AND THE OTHER INSTRUMENTS, DOCUMENTS AND
AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS AMENDMENT, 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.

         Executed as of the date first written above.

                                         BORROWER:

                                         SOUTH HAMPTON REFINING CO.

                                         BY: /s/ NICK CARTER
                                             ----------------------------------
                                             NICK CARTER
                                             President

                                      -5-

<PAGE>

                                         LENDER:

                                         SOUTHWEST BANK OF TEXAS, N.A.

                                         BY: /s/ A. STEPHEN KENNEDY
                                             ----------------------------------
                                             A. Stephen Kennedy
                                             Senior Vice President

         The undersigned Guarantor hereby consents and agrees to this Amendment
and agrees that the Guaranty Agreement executed by such person shall remain in
full force and effect and shall continue to be the legal, valid and binding
obligations of such Guarantor, enforceable against such Guarantor in accordance
with its terms and shall evidence such Guarantor's guaranty of the Note as
renewed and extended from time to time, including, without limitation, the
renewal and extension evidenced by the Note in substantially the form of Annex
"A" attached hereto.

                                         TEXAS OIL & CHEMICAL CO. II, INC.

                                         BY: /s/ NICK CARTER
                                             ----------------------------------
                                             NICK CARTER
                                             President

                                      -6-

<PAGE>

                                LIST OF ANNEXES

<Table>
<Caption>
            Annex                                          Document
            -----                                          --------
<S>                                                      <C>
              A                                            Note
</Table>

                                      -7-

<PAGE>

                                    ANNEX "A"

                                      Note
                                      ----

<PAGE>

                                PROMISSORY NOTE

$3,250,000.00                    Houston, Texas                 August 31, 2002

         FOR VALUE RECEIVED, the undersigned, SOUTH HAMPTON REFINING CO., a
Texas corporation ("Maker"), hereby promises to pay to the order of SOUTHWEST
BANK OF TEXAS, N.A., a national banking association ("Payee"), at its offices at
Five Post Oak Park, 4400 Post Oak Parkway, Houston, Harris County, Texas, or
such other address as may be designated by Payee, in lawful money of the United
States of America, the principal sum of THREE MILLION TWO HUNDRED FIFTY THOUSAND
AND NO/100 DOLLARS ($3,250,000.00), or so much thereof as may be advanced and
outstanding hereunder, together with interest on the outstanding principal
balance from day to day remaining, at a varying rate per annum which shall from
day to day be equal to the lesser of (a) the Maximum Rate (hereinafter defined)
or (b) the Prime Rate (hereinafter defined) of Payee in effect from day to day
plus one-half of one percent (.50%), and each change in the rate of interest
charged hereunder shall become effective, without notice to Maker, on the
effective date of each change in the Prime Rate or the Maximum Rate, as the case
may be; provided, however, if at any time the rate of interest specified in
clause (b) preceding shall exceed the Maximum Rate, thereby causing the interest
rate hereon to be limited to the Maximum Rate, then any subsequent reduction in
the Prime Rate shall not reduce the rate of interest hereon below the Maximum
Rate until the total amount of interest accrued hereon equals the amount of
interest which would have accrued hereon if the rate specified in clause (b)
preceding had at all times been in effect.

         Principal of and interest on this Note shall be due and payable as
follows:

                  (a) Accrued and unpaid interest on this Note shall be payable
         monthly, on the first (1st) day of each month commencing on September
         1, 2002 and upon the maturity of this Note, however such maturity may
         be brought about; and

                  (b) All outstanding principal of this Note and all accrued
         interest thereon shall be due and payable on December 31, 2002.

         Principal of this Note shall be subject to mandatory prepayment at the
times described in the Agreement (hereinafter defined). If an Event of Default
(hereinafter defined) has occurred and is existing, the principal hereof and any
past due interest hereon shall bear interest at the Default Rate (hereinafter
defined).

         Interest on the indebtedness evidenced by this Note shall be computed
on the basis of a year of 360 days and the actual number of days elapsed
(including the first day but excluding the last day) unless such calculation
would result in a usurious rate in which case interest shall be calculated on
the basis of a year of 365 or 366 days, as the case may be.

<PAGE>

         As used in this Note, the following terms shall have the respective
meanings indicated below:

                  "Agreement" means that certain Loan Agreement dated as of
         September 30, 1999 between Maker and Payee, as amended by First
         Amendment to Loan Agreement dated as of June 20, 2000, Second Amendment
         to Loan Agreement dated as of May 31, 2001, Third Amendment to Loan
         Agreement dated as of July 31, 2001, Fourth Amendment to Loan Agreement
         dated as of October 31, 2001, Fifth Amendment to Loan Agreement dated
         as of December 31, 2001, Sixth Amendment to Loan Agreement dated as of
         April 30, 2002 and Seventh Amendment to Loan Agreement dated as of
         August 31, 2002, as amended and as the same may be further amended or
         modified from time to time.

                  "Default Rate" means the lesser of (a) the sum of the Prime
         Rate plus five percent (5.0%), or (b) the Maximum Rate.

                  "Event of Default" shall have the meaning given to such term
         in the Agreement.

                  "Maximum Rate" means the maximum rate of nonusurious interest
         permitted from day to day by applicable law, including Chapter 303 of
         the Texas Finance Code (the "Code")(and as the same may be incorporated
         by reference in other Texas statutes). To the extent that Chapter 303
         of the Code is relevant to any holder of this Note for the purposes of
         determining the Maximum Rate, each such holder elects to determine such
         applicable legal rate pursuant to the "weekly ceiling," from time to
         time in effect, as referred to and defined in Chapter 303 of the Code;
         subject, however, to the limitations on such applicable ceiling
         referred to and defined in the Code, and further subject to any right
         such holder may have subsequently, under applicable law, to change the
         method of determining the Maximum Rate.

                  "Prime Rate" shall mean that variable rate of interest per
         annum established by Payee from time to time as its prime rate which
         shall vary from time to time. Such rate is set by Payee as a general
         reference rate of interest, taking into account such factors as Payee
         may deem appropriate, it being understood that many of Payee's
         commercial or other loans are priced in relation to such rate, that it
         is not necessarily the lowest or best rate charged to any customer and
         that Payee may make various commercial or other loans at rates of
         interest having no relationship to such rate.

         This Note (a) is the Note provided for in the Agreement and (b) is
secured as provided in the Agreement. Maker may prepay the principal of this
Note upon the terms and conditions specified in the Agreement. Maker may borrow,
repay, and reborrow hereunder upon the terms and conditions specified in the
Agreement.

                                      -2-

<PAGE>

         Notwithstanding anything to the contrary contained herein, no
provisions of this Note shall require the payment or permit the collection of
interest in excess of the Maximum Rate. If any excess of interest in such
respect is herein provided for, or shall be adjudicated to be so provided, in
this Note or otherwise in connection with this loan transaction, the provisions
of this paragraph shall govern and prevail, and neither Maker nor the sureties,
guarantors, successors or assigns of Maker shall be obligated to pay the excess
amount of such interest, or any other excess sum paid for the use, forbearance
or detention of sums loaned pursuant hereto. If for any reason interest in
excess of the Maximum Rate shall be deemed charged, required or permitted by any
court of competent jurisdiction, any such excess shall be applied as a payment
and reduction of the principal of indebtedness evidenced by this Note; and, if
the principal amount hereof has been paid in full, any remaining excess shall
forthwith be paid to Maker. In determining whether or not the interest paid or
payable exceeds the Maximum Rate, Maker and Payee shall, to the extent permitted
by applicable law, (a) characterize any non-principal payment as an expense,
fee, or premium rather than as interest, (b) exclude voluntary prepayments and
the effects thereof, and (c) amortize, prorate, allocate, and spread in equal or
unequal parts the total amount of interest throughout the entire contemplated
term of the indebtedness evidenced by this Note so that the interest for the
entire term does not exceed the Maximum Rate.

         If default occurs in the payment of principal or interest under this
Note, or upon the occurrence of any other Event of Default, as such term is
defined in the Agreement the holder hereof may, at its option, (a) declare the
entire unpaid principal of and accrued interest on this Note immediately due and
payable without notice, demand or presentment, all of which are hereby waived,
and upon such declaration, the same shall become and shall be immediately due
and payable, (b) foreclose or otherwise enforce all liens or security interests
securing payment hereof, or any part hereof, (c) offset against this Note any
sum or sums owed by the holder hereof to Maker and (d) take any and all other
actions available to Payee under this Note, the Agreement, the Loan Documents
(as such term is defined in the Agreement) at law, in equity or otherwise.
Failure of the holder hereof to exercise any of the foregoing options shall not
constitute a waiver of the right to exercise the same upon the occurrence of a
subsequent Event of Default.

         If the holder hereof expends any effort in any attempt to enforce
payment of all or any part or installment of any sum due the holder hereunder,
or if this Note is placed in the hands of an attorney for collection, or if it
is collected through any legal proceedings, Maker agrees to pay all costs,
expenses, and fees incurred by the holder, including all reasonable attorneys'
fees.

         THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
LAWS OF THE STATE OF TEXAS AND THE APPLICABLE LAWS OF THE UNITED STATES OF
AMERICA. THIS NOTE IS PERFORMABLE IN HARRIS COUNTY, TEXAS.

                                      -3-

<PAGE>

         Maker and each surety, guarantor, endorser, and other party ever liable
for payment of any sums of money payable on this Note jointly and severally
waive notice, presentment, demand for payment, protest, notice of protest and
non-payment or dishonor, notice of acceleration, notice of intent to accelerate,
notice of intent to demand, diligence in collecting, grace, and all other
formalities of any kind, and consent to all extensions without notice for any
period or periods of time and partial payments, before or after maturity, and
any impairment of any collateral securing this Note, all without prejudice to
the holder. The holder shall similarly have the right to deal in any way, at
any time, with one or more of the foregoing parties without notice to any other
party, and to grant any such party any extensions of time for payment of any of
said indebtedness, or to release or substitute part or all of the collateral
securing this Note, or to grant any other indulgences or forbearances
whatsoever, without notice to any other party and without in any way affecting
the personal liability of any party hereunder.

         This Note is in renewal and extension of, but not in discharge or
novation of, that certain promissory note in the original principal amount of
$3,250,000.00, dated April 30, 2002, executed by Maker and payable to the order
of Payee, which was executed in renewal and extension of, but not in discharge
or novation of, that certain promissory note in the original principal amount of
$3,250,000.00, dated December 31, 2001, executed by Maker and payable to the
order of Payee, which was executed in renewal and extension of, but not in
discharge or novation of, that certain promissory note in the original principal
amount of $3,250,000.00, dated October 31, 2001, executed by Maker and payable
to the order of Payee, which was executed in renewal and extension of, but not
in discharge or novation of that certain promissory note in the original
principal amount of $3,250,000.00, dated July 31, 2001, executed by Maker and
payable to the order of Payee, which was executed in renewal and extension of,
but not in discharge or novation of, that certain promissory note in the
original principal amount of $3,250,000.00, dated May 31, 2001, executed by
Maker and payable to the order of Payee, which was executed in renewal and
extension of, but not in discharge or novation of, that certain promissory note
in the original principal amount of $3,250,000.00, dated June 20, 2000, executed
by Maker and payable to the order of Payee, which was executed in renewal and
increase of, but not in discharge or novation of, that certain promissory note
in the original principal amount of $2,250,000.00, dated September 30, 1999,
executed by Maker and payable to the order of Payee.

                                            SOUTH HAMPTON REFINING CO.

                                            By: /s/ NICK CARTER
                                                -------------------------------
                                                Nick Carter
                                                President

                                      -4-

<PAGE>

                           SOUTH HAMPTON REFINING CO.

                              OFFICER'S CERTIFICATE

         I, the undersigned, hereby certify that I am the duly elected,
qualified, and acting Assistant Secretary of SOUTH HAMPTON REFINING CO., a Texas
corporation (the "Corporation"), and that I am authorized to execute and deliver
this certificate, and I do hereby further certify as follows:

         1. Resolutions. The following resolutions have been duly adopted at a
meeting (duly convened where a quorum of directors was present) of, or by the
unanimous written consent of, the Board of Directors of the Corporation, and
such resolutions have not been amended or revoked, and are now in full force and
effect:

                  "WHEREAS, the Corporation and Southwest Bank of Texas, N.A.
         (the "Lender") have entered in that certain Loan Agreement dated
         September 30, 1999, as amended by First Amendment to Loan Agreement
         dated June 20, 2000, Second Amendment to Loan Agreement dated May
         31, 2001, Third Amendment to Loan Agreement dated July 31, 2001, Fourth
         Amendment to Loan Agreement dated October 31, 2001, Fifth Amendment to
         Loan Agreement dated December 31, 2001 and Sixth Amendment to Loan
         Agreement dated April 30, 2002 (collectively, the "Loan Agreement")."

                  "RESOLVED, that the renewal and extension of the revolving
         credit indebtedness of the Corporation to the Lender created pursuant
         to the Loan Agreement to be evidenced by a promissory note in the
         principal amount of $3,250,000.00 (the "Note") executed by the
         Corporation and payable to the order of the Lender, is hereby approved;
         and further

                  "RESOLVED, that the form and content of that certain Seventh
         Amendment to Loan Agreement (the "Amendment") to be entered into by the
         Corporation and the Lender in the form of drafts exhibited to each
         director, with such changes as are hereinafter authorized, are hereby
         approved; and further

                  "RESOLVED, that the form and content of the Note and all other
         documents to be executed in connection with the Amendment
         (collectively, the "Loan Documents"), as exhibited to each director and
         with such changes as are hereinafter authorized, are hereby approved;
         and further

                  "RESOLVED, that the President or any Vice President of the
         Corporation is hereby authorized, on behalf of the Corporation, to
         execute the Amendment and the Loan Documents and deliver the same to
         Lender in substantially the form approved by these resolutions, with
         such amendments or changes thereto as the officer so acting

<PAGE>

         may approve, such approval to be conclusively evidenced by such
         person's execution and delivery of the same; and further

                  "RESOLVED, that the President or any Vice President of the
         Corporation is hereby authorized, on behalf of the Corporation, to
         execute such other instruments and documents, and to take such other
         actions as the officer so acting deems necessary or desirable to
         effectuate the transactions contemplated by these resolutions; and
         further

                  "RESOLVED, that the Secretary or any Assistant Secretary of
         the Corporation is hereby authorized, on behalf of the Corporation, to
         certify and attest any documents which such person may deem necessary
         or appropriate to consummate the transactions contemplated by these
         resolutions; provided that such attestation shall not be required for
         the validity of any such documents; and further

                  "RESOLVED, that any and all actions taken by any of the
         officers or representatives of the Corporation, for and on behalf and
         in the name of the Corporation, with Lender prior to the adoption of
         these resolutions, including, without limitation, the negotiation of
         the Amendment and the Loan Documents, are hereby ratified, confirmed,
         are approved in all respects for all purposes; and further

                  "RESOLVED, that the powers and authorizations contained herein
         shall continue in full force and effect until written notice of
         revocation has been given to, and received by, the Lender."

         2. Incumbency. The following named persons are duly elected or
appointed, acting, and qualified officers of the Corporation holding at the date
hereof the offices set forth opposite their respective names, and the signatures
appearing opposite their respective names are their genuine signatures:

<Table>
<Caption>
    NAME                                      TITLE                       SPECIMEN SIGNATURE
    ----                                      -----                       ------------------
<S>                                  <C>                                <C>
Nick Carter                                 President                      /s/ NICK CARTER
                                                                        -----------------------
Connie Cook                          Assistant Secretary                    /s/ CONNIE COOK
                                                                        -----------------------
</Table>

         3. Articles of Incorporation. The Articles of Incorporation of the
Corporation have not been amended (except as reflected in any attachments
hereto) or revoked since September 30, 1999, and remain in full force and effect
in the form delivered to the Lender.

         4. By-Laws. The By-Laws of the Corporation have not been amended
(except as reflected in any attachments hereto) or revoked since September 30,
1999, and remain in full force and effect in the form delivered to the Lender.

                                      -2-

<PAGE>

         IN WITNESS WHEREOF, I have duly executed this certificate as of
September 30th, 2002.

                                                      /s/ CONNIE COOK
                                              ---------------------------------
                                              Assistant Secretary

         I, Nick Carter, President of the Corporation, do hereby certify that
Connie Cook is the duly elected and qualified Assistant Secretary of the
Corporation and the signature appearing opposite such person's name is such
person's genuine signature.

         DATED: As of September 30, 2002.

                                                      /s/ NICK CARTER
                                              ---------------------------------
                                              President

                                      -3-<PAGE>
                                                                    EXHIBIT 4.28

September 12, 2002

Jackson Walker L.L.P.
2435 N. Central Expressway, Suite 600
Richardson, Texas 75080

         Attn: Richard F. Dahlson, Partner

Dear Rick:

         Mobility Electronics, Inc., a Delaware corporation (the "Company"), and
Jackson Walker L.L.P. ("JW") are parties to a letter agreement, dated as of
August 7, 2002 (the "Prior Agreement"). This letter agreement supercedes the
Prior Agreement, and the Prior Agreement shall be deemed to be of no further
force or effect. The Company currently owes JW the sum of $868,988.69 for legal
services and fees with respect to JW's invoice numbers 694093 (dated April 26,
2002), 699105 (dated May 23, 2002), 703685 (dated June 21, 2002), 705742 (dated
July 19, 2002), 711952 (dated August 16, 2002) and 716799 (to be dated September
17, 2002) (collectively, the "Owed Fees"). The Company acknowledges and agrees
that it owes the Owed Fees to JW and has no dispute or claim against JW with
respect to the Owed Fees. The Company desires for JW to convert $600,000 of the
Owed Fees (the "Convertible Fees") into 571,428 shares (the "Shares") of common
stock, par value $0.01 per share, of Mobility (the "Common Stock"), and JW is
agreeable to such request on the terms and conditions set forth below.

         For good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged and agreed, the Company and JW hereby agree as
follows:

         1. If on or prior to December 5, 2002 (the "Deadline"), the Company has
filed a registration statement (the "Registration Statement") with the
Securities and Exchange Commission (the "SEC") which registers the resale of the
Shares by JW, and the Registration Statement has been declared effective by the
SEC (the "Effective Date"), then the Convertible Fees shall automatically be
deemed to be converted into the Shares as of the Effective Date, and within five
(5) business days after the Effective Date, the Company will cause its transfer
agent to deliver to JW a certificate representing the Shares (or, at JW's
discretion, the transfer agent will cause the Shares to be DTC transferred into
JW's brokerage account).

         2. If the Registration Statement has not been declared effective by the
SEC on or prior to December 5, 2002, then on December 6, 2002 the Company shall
wire transfer to JW the sum of $600,000 as payment for the $600,000 of the
Convertible Fees not so converted pursuant to Section 1 above.

         3. If the average closing price of the Common Stock for the period
between the Effective Date and December 31, 2002 (the "Average Closing Price"),
does not exceed $1.16 per share, then on or prior to January 10, 2003, the
Company shall pay to JW by wire transfer an amount equal to the difference
between $1.16 and the Average Closing Price, less an amount equal to the amounts
received by JW (net of commissions) from the sale of Shares from the

<PAGE>

Richard F. Dahlson
September 12, 2002
Page 2

Effective Date to December 31, 2002, in excess of the product of $1.16 per Share
multiplied by the number of Shares sold during such period.

         4. On October 1, 2002, the Company shall wire transfer to JW the
$268,988.69 of the Owed Fees which are not included in the Convertible Fees.

         5. This letter may be executed in two or more counterparts, each of
which shall be deemed to be an original but all of which shall constitute one
and the same instrument. If the terms set forth in this letter agreement are
acceptable to you, please sign and date the enclosed copy of this letter and
return it to the Company.

                                                MOBILITY ELECTRONICS, INC.

                                                By: /s/Joan W. Brubacher
                                                    ----------------------------
                                                    Joan W. Brubacher,
                                                    Chief Financial Officer

AGREED TO AND ACCEPTED
as of the date first above written:

JACKSON WALKER L.L.P.

By: /s/Richard F. Dahlson
    --------------------------------
    Richard F. Dahlson, Partner

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