Document:

<PAGE>   1
                                                                    EXHIBIT 10.5

                         NON-NEGOTIABLE PROMISSORY NOTE

$1,000,000.00                                                      July 27, 2001
                                                                DENVER, COLORADO

         FOR VALUE RECEIVED, the undersigned, TREMONT CORPORATION, a Delaware
corporation ("Maker"), promises to pay to the order of J. LANDIS MARTIN
("Executive"), at the offices of Maker at 1999 Broadway, Suite 4300, Denver, CO
80202 or such other place as Executive may designate in writing to Maker, the
principal sum of ONE MILLION DOLLARS ($1,000,000.00) of United States funds, or,
if less, so much thereof as may be outstanding from time to time, plus interest
as hereinafter provided.

         Maker hereby promises to pay to Executive the unpaid principal amount
in five (5) equal annual installments on June 12 of each year commencing on June
12, 2002, with all unpaid principal and interest due and payable on June 12,
2006 (the "Maturity Date"); provided, however, if the payment of such amount at
such time would not be deductible to Maker for tax purposes under the provisions
of Section 162(m) of the Internal Revenue Code of 1986, as amended, or any
successor provision, Maker may defer such payment until the earliest time at
which the payment of such amount would be deductible by Maker. Maker, acting
through its Management Development & Compensation Committee, may elect, in its
sole discretion, to make payment of all or any portion of the principal prior to
the Maturity Date without penalty or premium.

         Maker hereby promises to pay interest on the unpaid principal amount
hereof at a rate per annum equal to seven percent (7.0%) from June 12, 2001 up
to and including the date of payment. Interest accrued on the unpaid principal
shall be payable at the time of payment to Executive of each annual installment
of principal pursuant to the immediately preceding paragraph. Interest accrued
pursuant to this paragraph shall compound on a semi-annual basis on January 1
and July 1 and shall be computed for the actual number of days elapsed on the
basis of a year consisting of 365 or 366 days, as applicable. Overdue principal
and, to the extent permitted by law, overdue interest, shall bear interest
payable on DEMAND at a rate of ten percent (10%) per annum from the date payment
was due until and including the date actually paid (it being recognized that any
principal or interest the payment of which is deferred by Maker pursuant to the
proviso of the immediately preceding paragraph for tax reasons shall
nevertheless be regarded as overdue).

         In no event shall the amount of interest due or payable hereunder
exceed the maximum rate of interest allowed by applicable law, and in the event
any such payment is inadvertently made by Maker or inadvertently received by
Executive, then such excess sum shall be credited as a payment of principal,
unless Maker shall notify Executive in writing that it elects to have such
excess sum returned forthwith. It is the express intent of the parties that
Maker not pay and Executive not receive, directly or indirectly in any manner
whatsoever, interest in excess of that which may legally be paid by Maker under
applicable law.

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<PAGE>   2

         Maker shall withhold from any amounts paid to Executive pursuant to
this Note, in the year such amount is paid to Executive, or from any salary,
bonus or other compensatory payment made to Executive as Maker in its sole
discretion may determine, such amounts as are required by law to be withheld
pursuant to any applicable withholding requirements.

         All parties now or hereafter liable with respect to this Note, whether
Maker, any guarantor, endorser, or any other person, hereby waive presentment
for payment, demand, notice of non-payment or dishonor, protest and notice of
protest.

         No delay or omission on the part of Executive or any holder hereof in
exercising his or its rights under this Note or course of conduct relating
thereto, shall operate as a waiver of such rights or any other right of
Executive or any holder hereof, nor shall any waiver of any such right or rights
on any one occasion be deemed a bar to, or waiver of, the same right or rights
on any future occasion.

         Maker promises to pay all reasonable costs of collection, including
attorneys' fees and expenses, should this Note be collected by or through an
attorney-at-law or under advice therefrom.

         Time is of the essence of this Note.

         This Note is non-negotiable.

         This Note shall be construed in accordance with and governed by the
internal laws of the state of Colorado.

         IN WITNESS WHEREOF, Maker has executed this Note on the day and year
first above written, but with effect as of June 12, 2001.

                                             MAKER:

                                             TREMONT CORPORATION

                                             By: /s/Robert E Musgraves
                                                --------------------------------

                                             Its: Vice President
                                                 -------------------------------

                                       2<PAGE>   1
                                                                   EXHIBIT 10(a)

                                    AGREEMENT

         This Agreement ("Agreement") is made and entered into as of the lst day
of April, 2001 by and between South Hampton Refining Co., a Texas corporation,
Gulf State Pipe Line Company, Inc., a Texas corporation ("Borrowers") and Heller
Financial Leasing, Inc., a Delaware corporation, ("Heller").

         WHEREAS, Heller and Borrowers are parties to that certain Loan and
Security Agreement dated December 30, 1999, and all amendments thereto ("Loan
Agreement"), which is secured by that certain Promissory Note, dated December
30, 1999 (the "Note"), in the original principal amount of Three Million Five
Hundred Thousand and 00/100 Dollars ($3,500,000.00); and

         WHEREAS, on or about December 1, 2000, Borrowers failed to make their
monthly installment payment to Heller under the Note, which constituted an Event
of Default pursuant to Section 7 of the Loan Agreement;

         WHEREAS, on or about January 19, 2001, Heller agreed to suspend
Borrowers principal payments only for the months of December 2000, January,
February and March of 2001 until April 1, 2001;

         WHEREAS, the Borrowers have requested an adjustment in the principal
payments; and

         WHEREAS, the parties hereto desire to amend the Note;

         NOW, THEREFORE, in consideration of the mutual conditions and
agreements set forth in the Loan Agreement and this Agreement and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

         1. Definitions. Capitalized terms used in this Agreement, unless
otherwise defined herein, shall have the meaning ascribed to such term in the
Loan Agreement.

         2. Amendments. Heller hereby agrees to amend and restate the Note to
reflect the change in the principal payments.

         3. Conditions. The effectiveness of this Agreement is subject to the
following conditions precedent (unless specifically waived in writing by
Heller):

            (a) There shall have occurred no material adverse change in the
business, operations, financial condition, profits or prospects of Borrowers or
in the Collateral;

            (b) Borrowers shall have executed and delivered such other documents
and instruments as Heller may require;

            (c) All proceedings taken in connection with the transactions
contemplated by this Agreement and all documents, instruments and other legal
matters incident thereto shall be satisfactory to Heller and its legal counsel;

            (d) No Default or Event of Default under the Loan Agreement as
amended hereby shall have occurred and be continuing; and

<PAGE>   2

            4. Fee. Borrowers agree to pay Heller an amendment fee in the amount
of $15,000.00, which shall be payable in three (3) consecutive monthly
installments, in the amount of $5,000.00, beginning on May 1, 2001.

            5. Corporate Action. The execution, delivery, and performance of
this Agreement has been duly authorized by all requisite corporate action on the
part of Borrowers and this Agreement has been duly executed and delivered by
Borrowers.

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

            7. References. Any reference to the Loan Agreement contained in any
notice, request, certificate, or other document executed concurrently with or
after the execution and delivery of this Agreement shall be deemed to include
this Agreement unless the context shall otherwise require.

            8. Counterparts. This Agreement may be executed in one or more
counterparts, each of which shall constitute an original, but all of which taken
together shall be one and the same instrument.

            9. Ratification. The terms and provisions set forth in this
Agreement shall modify and supersede all inconsistent terms and provisions of
the Loan Agreement and, except as expressly modified and superseded by this
Agreement, the terms and provisions of the Loan Agreement are ratified and
confirmed and shall continue in full force and effect.

            IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed under seal and delivered by their respective duly authorized
officers on the date first written above.

HELLER FINANCIAL LEASING, INC.

By: /s/ RONALD E. LIS
   ----------------------------------
Name: Ronald E. Lis
     --------------------------------
Its: Vice President
    ---------------------------------

SOUTH HAMPTON REFINING, CO.

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

GULF STATE PIPE LINE COMPANY, INC.

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

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<PAGE>   3

                            CONSENT AND REAFFIRMATION

The undersigned Guarantors of the Indebtedness of Borrowers at any time owing to
Heller hereby (i) acknowledge receipt of a copy of the foregoing Agreement; (ii)
consent to Borrowers' execution and delivery thereof; (iii) agree to be bound
thereby; and (iv) affirm that nothing contained therein shall modify in any
respect whatsoever their guaranty of the obligations and reaffirms that such
guaranty is and shall remain in full force and effect. Although Guarantors have
been informed of the matters set forth herein and have acknowledged and agreed
to same, Guarantors understand that Heller has no obligation to inform
Guarantors of such matters in the future or to seek Guarantors' acknowledgment
or agreement to future amendments or waivers, and nothing herein shall create
such a duty.

         IN WITNESS WHEREOF, the undersigned have executed this Consent and
Reaffirmation on and as of the date of such Agreement.

                                    TEXAS OIL AND CHEMICAL CO. II, INC.

                                    By: /s/ NICK CARTER
                                       ----------------------------------
                                    Name: NICK CARTER
                                         --------------------------------
                                    Its: President
                                        ---------------------------------

                                    ARABIAN SHIELD DEVELOPMENT COMPANY

                                    By: /s/ HATEM EL-KHALIDI
                                       ----------------------------------
                                    Name: HATEM EL-KHALIDI
                                         --------------------------------
                                    Its: President & CEO
                                        ---------------------------------

                                    AMERICAN SHIELD REFINING COMPANY

                                    By: /s/ HATEM EL-KHALIDI
                                       ----------------------------------
                                    Name: HATEM EL-KHALIDI
                                         --------------------------------
                                    Its: President
                                        ---------------------------------

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<PAGE>   4

                                                          Loan No.: 192-0280-001
                              AMENDED AND RESTATED

                                 PROMISSORY NOTE

$1,627,036.28                                                      April 1, 2001

         FOR VALUE RECEIVED, SOUTH HAMPTON REFINING CO., a Texas corporation and
GULF STATE PIPE LINE COMPANY, INC., a Texas corporation (collectively,
"Maker"), promises to pay to the order of HELLER FINANCIAL LEASING, INC., a
Delaware corporation (together with any holder of this Note, "Payee"), at its
office located at 500 West Monroe Street, Chicago, Illinois 60661, or at such
other place as Payee may from time to time designate, the principal sum of One
Million Six Hundred Twenty Seven Thousand Thirty Six and 00/100
($1,627,036.28), together with interest thereon at a fixed rate equal to 10.55%
per annum. Maker shall make an interest only payment on April 1, 2001. Twenty
Five Thousand and 00/100 Dollars ($25,000.00) plus interest shall be payable in
two (2) consecutive monthly installments commencing on May 1, 2001, and
principal and interest shall be payable in thirty-one (31) consecutive monthly
installments commencing July 1, 2001, and continuing on the same day of each
consecutive calendar month thereafter until this Note is fully paid, each such
installment in the amount of Fifty Eight Thousand Three Hundred and Forty and
96/100 ($58,340.96); provided, however, that in any and all events the final
installment payment hereunder shall be in the amount of the entire then
outstanding principal balance hereunder, plus all accrued and unpaid interest,
charges and other amounts owing hereunder or under the Security Agreement
(defined below). All payments shall be applied first to interest and then to
principal. Interest shall be computed on the basis of a 360 day year comprised
of 30-day months.

         It is the intent of the parties to comply strictly with applicable
usury laws. Notwithstanding anything herein to the contrary, in no event shall
interest contracted for, taken, charged, reserved or received hereunder ever
exceed the highest non-usurious interest permitted under applicable law and if
any such excess interest is taken, received or collected, then such excess shall
be deemed the result of a mathematical error and shall be applied as a reduction
of principal and any remainder refunded to the Maker.

         This Note is secured by the collateral described in the Loan and
Security Agreement dated December 30, 1999, between Maker and Payee (the
"Security Agreement;" and together with all related documents and instruments,
the "Loan Documents") to which reference is made for a statement of the nature
and extent of protection and security afforded, certain rights of Payee and
certain rights and obligations of Maker.

         Upon 45 days prior written notice to Payee, Maker may prepay in whole,
but not in part, the then entire unpaid principal balance of this Note, together
with all accrued and unpaid interest thereon to the date of such prepayment,
provided that in addition to such prepayment, Maker shall pay (i) any and all
other sums then due under any of the Loan Documents, plus (ii) the Prepayment
Fee (defined below), plus (iii) the Breakage Fee (defined below). As used herein
the term "Prepayment Fee" means a sum equal to 1% of the principal balance
prepaid for each full or partial 12 month period by which the date of the
prepayment precedes the scheduled due date of the final installment of principal
hereunder. As used herein, the term "Breakage Fee" shall mean the amount, if
any, by which (A) the present value, in the aggregate, of the then remaining
installments of principal and interest due hereunder, absent the prepayment,
using a discount rate equal to the yield to maturity as of the date two days
prior to the date of the prepayment on United States Treasury securities with a
final maturity approximately equal to the remaining term hereof, absent the
prepayment, as published in The Wall Street Journal, exceeds (B) the then
outstanding principal balance hereunder, absent the prepayment. The Prepayment
Fee and the Breakage Fee represent liquidated damages to Payee for the loss of
its bargain and not penalties. The Prepayment Fee and The Breakage Fee shall
also be due upon the acceleration of the maturity date hereof following the
occurrence of any Event of Default (as defined in the Security Agreement).

         Time is of the essence hereof. If payment of any installment or any
other sum due under this Note or the Loan Documents is not paid when due, Maker
agrees to pay a late charge equal to the lesser of (i) five cents per dollar on,
and in addition to, the amount of each such payment, or (ii) the maximum amount
Payee is permitted to charge by law. In the event of the occurrence of an Event
of Default (as defined in the Security Agreement), then the entire unpaid
principal balance hereof with accrued and unpaid interest thereon, together with
all other sums payable under this Note or the Loan Documents, shall, at the
option of Payee and without notice or demand, become immediately due and
payable, such accelerated balance bearing interest until paid at the rate of
5.00% per annum above the then otherwise applicable interest rate hereunder.

         Maker and all endorsers, guarantors or any others who may at any time
become liable for the payment hereof hereby consent to any and all extensions of
time, renewals, waivers and modifications of, and substitutions or release of
security or of any party primarily or secondarily liable on, or with respect to,
this Note or any of the Loan Documents or any of the terms and provisions
thereof that may be made, granted or consented to by Payee, and agree that suit
may be brought and maintained against any one or more of them, at the election
of Payee, without joinder of the others as parties thereto, and that Payee shall
not be required to first foreclose, proceed against, or exhaust any security
herefor, in order to enforce payment of this Note by any one or more of them.
Maker and all endorsers, guarantors or any others who may at any time become
liable for the payment hereof hereby severally waive presentment, demand for
payment, notice of nonpayment, protest, notice of protest, notice of dishonor,
and all other notices in connection with this Note, filing of suit and diligence
in collecting this Note or enforcing any of the security herefor, and, without
limiting any provision of any of the Loan Documents, agree to pay, if permitted
by law, all expenses incurred in collection, including reasonable attorneys'
fees, and hereby waive all benefits of valuation, appraisement and exemption
laws.

         THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE
INTERNAL LAWS AND DECISIONS OF THE STATE OF ILLINOIS, WITHOUT REGARD TO
PRINCIPLES OF CONFLICTS OF LAW. AT PAYEE'S

<PAGE>   5

ELECTION AND WITHOUT LIMITING PAYEE'S RIGHT TO COMMENCE AN ACTION IN ANY OTHER
JURISDICTION, MAKER HEREBY SUBMITS TO THE EXCLUSIVE JURISDICTION AND VENUE OF
ANY COURT (FEDERAL, STATE OR LOCAL) HAVING SITUS WITHIN THE STATE OF ILLINOIS,
EXPRESSLY WAIVES PERSONAL SERVICE OF PROCESS AND CONSENTS TO SERVICE BY
CERTIFIED MAIL, POSTAGE PREPAID, DIRECTED TO THE LAST KNOWN ADDRESS OF MAKER,
WHICH SERVICE SHALL BE DEEMED COMPLETED WITHIN TEN DAYS AFTER THE DATE OF
MAILING THEREOF.

         MAKER HEREBY WAIVES ITS RIGHTS TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF
ACTION BASED UPON OR ARISING OUT OF THIS NOTE. THIS WAIVER IS INFORMED AND
FREELY MADE. MAKER ACKNOWLEDGES THAT THIS WAIVER IS A MATERIAL INDUCEMENT TO
ENTER INTO A BUSINESS RELATIONSHIP, THAT PAYEE HAS ALREADY RELIED ON THE WAIVER
IN MAKING THE LOAN EVIDENCED BY THIS NOTE, AND THAT PAYEE WILL CONTINUE TO RELY
ON THE WAIVER IN ITS RELATED FUTURE DEALINGS. MAKER FURTHER WARRANTS AND
REPRESENTS THAT IT HAS REVIEWED THIS WAIVER WITH ITS LEGAL COUNSEL AND THAT IT
KNOWINGLY AND VOLUNTARILY WAIVES ITS JURY TRIAL RIGHTS FOLLOWING CONSULTATION
WITH LEGAL COUNSEL.

WITNESS/ATTEST                  SOUTH HAMPTON REFINING CO., a Texas corporation

/s/ CONNIE COOK                 By: /s/ NICK CARTER
----------------------             -----------------------------
                                Name: Nick Carter
                                     ---------------------------
WITNESS/ATTEST                  Title: President
                                      --------------------------
/s/ CONNIE COOK
----------------------          GULF STATE PIPE LINE COMPANY, INC.,
                                a Texas corporation

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

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