Document:

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                                AMENDMENT NO. 1

                                      TO

                           PRODUCT SUPPLY AGREEMENT

     This Amendment No. 1 is effective 1 March 2000 by and between, AIR PRODUCTS
AND CHEMICALS, INC., a corporation organized and existing under the laws of the
State of Delaware (hereinafter called "Seller"), and CLARK REFINING & MARKETING,
INC., a corporation organized and existing under the laws of the State of
Delaware (hereinafter called "Buyer").

                               WITNESSETH THAT:

     WHEREAS, Seller and Buyer are parties to a Product Supply Agreement dated
as of 1 August 1999 (hereinafter referred to as the "Agreement"); and

     WHEREAS, the parties now wish to further amend the Agreement as set forth
herein.

     NOW, THEREFORE, in consideration of the foregoing and the terms and
conditions set forth herein, Seller and Buyer agree to amend the Agreement as
follows:

1.   In Section 4.1.9 Density Determination, delete the first sentence in this
section in its entirety and replace with the following sentence: "The flowing
gas density of the refinery fuel gas stream shall be determined using an on-line
gas chromatograph."

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2.   Delete Section 4.1.15 Calibration of Gas Densitometer in its entirety.

3.   In Appendix I, delete in its entirety the paragraph beginning "LHVrf and
HHVrf shall be as calculated..." and replace it with the following:

"LHVrf and HHVrf shall be calculated monthly by Seller based on averaging
Seller's gas chromatograph-based determination of the refinery fuel heating
values. LHVng and HHVng shall be the monthly average values of each as provided
by the supplier(s) of natural gas. The quantity of BTU's purchased by Seller
from Buyer shall be determined by Seller's metering and chromatograph on a
BTU/month, HHV basis."

4.   All defined terms set forth herein without definition shall have the
meaning given such term in the Agreement.

5.   Except as set forth herein, all other terms and conditions of the
Agreement shall remain unchanged and continue in full force and effect.

     IN WITNESS WHEREOF, parties hereto have caused this Amendment No. 1 to be
executed by their duly authorized officers as of the date first written above.

                                       AIR PRODUCTS AND CHEMICALS, INC.

                                       By: /s/ John Xxxxxx
                                           ----------------------------
                                       Title: Vice President
                                              -------------------------

                                       CLARK REFINING & MARKETING, INC.

                                       By: /s/ Ken Xxxxxx
                                           ----------------------------
                                       Title: Technical Manager
                                              -------------------------
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                                AMENDMENT NO. 1

                                      TO

                           HYDROGEN SUPPLY AGREEMENT

     This Amendment No. 1 is effective 1 March 2000 by and between, AIR PRODUCTS
AND CHEMICALS, INC., a corporation organized and existing under the laws of the
State of Delaware (hereinafter called "Seller"), and PORT ARTHUR COKER COMPANY
L.P., a limited partnership organized and existing under the laws of the State
of Delaware (hereinafter called "Buyer").

                               WITNESSETH THAT:

     WHEREAS, Seller and Buyer are parties to a Hydrogen Supply Agreement dated
as of 1 August 1999 (hereinafter referred to as the "Agreement"); and

     WHEREAS, the parties now wish to further amend the Agreement as set forth
herein.

     NOW, THEREFORE, in consideration of the foregoing and the terms and
conditions set forth herein, Seller and Buyer agree to amend the Agreement as
follows:

1.   Delete Section 7.6 One Time Charges in its entirety and replace with the
following:

     "Section 7.6 One Time Charges. No later than 1 September 2000, Buyer shall
pay Seller a lump sum for each of the following items:

<TABLE>
          <S>                                                 <C>
          Flare Stack                                         $521,180
          Control Building Protection                         $296,640
          Senior Orifice Meter Run for Refinery Fuel Gas      $ 26,800
          H\\2\\S Analyzer for Spill Gas Feed                 $ 56,700"
</TABLE>

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2.   In Appendix 1, delete in its entirety the paragraph beginning "LHVrf and
HHVrf shall be calculated..." and replace it with the following:

"LHVrf and HHVrf shall be calculated monthly by Seller based on averaging
Seller's gas chromatograph-based determination of the refinery fuel heating
values. LHVng and HHVng shall be the monthly average values of each as provided
by the supplier(s) of natural gas. The quantity of BTU's purchased by Seller
from Clark shall be determined by Seller's metering and chromatograph on a
BTU/month, HHV basis."

3.   All defined terms set forth herein without definition shall have the
meaning given such term in the Agreement.

4.   Except as set forth herein, all other terms and conditions of the
Agreement shall remain unchanged and continue in full force and effect.

     IN WITNESS WHEREOF, parties hereto have caused this Agreement No. 1 to be
executed by their duly authorized officers as of the date first written above.

                                       AIR PRODUCTS AND CHEMICALS, INC.

                                       By: /s/ John Xxxxxx
                                           ----------------------------
                                       Title: Vice President
                                       -------------------------

                                       PORT ARTHUR COKER COMPANY L.P.

                                       By: SABINE RIVER HOLDING CORP.,
                                           as General Partner

                                       By: /s/ Ken Xxxxxx
                                           ----------------------------
                                       Title: Vice President
                                              -------------------------<PAGE>

                                AMENDMENT NO. 2
                                      TO
                           HYDROGEN SUPPLY AGREEMENT

          This Amendment No. 2 is effective 1 June, 2001, by and between Port
Arthur Coker Company L.P., a limited partnership organized and existing under
the laws of the State of Delaware (hereinafter referred to as "Buyer") and Air
Products and Chemicals, Inc., a corporation organized and existing under the
laws of the State of Delaware (hereinafter referred to as "Seller").

                               WITNESSETH THAT:

WHEREAS, Seller and Buyer are parties to a Hydrogen Supply Agreement dated as of
1 August 1999 (hereinafter referred to as the "Agreement"); and

WHEREAS, the parties now wish to further amend the Agreement as set forth
herein.

NOW, THEREFORE, in consideration of the forgoing and the terms and conditions
set forth herein, Seller and Buyer agree to amend the Agreement as follows:

1.   Add new Section 12.3, as follows:

"12.3 Indemnification. Nothing herein shall be construed to require Seller to
take any action to attempt to secure a reduction in Buyer's Pro Rata Share of
property taxes, ad valorem taxes and payments under the Property Tax Agreements
(hereinafter referred to as an "Action") if, in the judgment of Seller's Vice
President, Taxes or his designee, such Action could have a potential adverse
impact upon Seller, including an increase in assessed value and/or an increase
in the Seller's portion of property taxes, ad valorem taxes and payments under
the Property Tax Agreements. Notwithstanding the forgoing, in the event that
Buyer should reasonably request that Seller take such Action, and Seller agrees
to comply, then the following provisions shall apply:

          (A) It is agreed that Seller shall be entitled for reimbursement for
any costs and expenses that it may incur with respect to an Action. In the event
that Seller, in its absolute discretion, shall seek such reimbursement, then
Buyer shall reimburse Seller for (i) all costs and expenses of any type and
nature incurred by Seller as a result of or relating to taking of such Action
and (ii) the actual cost (including wages, benefits, overhead, etc.) of time
spent by Seller's employees dealing with the Action.

          (B) Without limitation to the foregoing, Buyer shall pay for, defend,
with counsel satisfactory to Seller, protect, indemnify and save harmless Seller
from and against any and all liabilities, obligations, claims, investigations,
inquiries, judgments,
<PAGE>

damages, penalties, causes of action, costs and expenses (including, without
limitation, attorneys' fees and expenses) imposed upon or incurred by or
asserted against Seller by reason of (i) taking an Action, (ii) any
misrepresentation by Buyer hereunder, or (iii) any failure on the part of the
Buyer to perform or observe any of its agreements or obligations under this
Agreement. For purposes of this Section 12.3, any increase in property taxes, ad
valorem taxes or payments under the Property Tax Agreements over and above that
which Seller would have been required to have paid but for Buyer's request that
Seller take an Action shall be considered to be an indemnifiable expense
hereunder.

          (C) Without limitation to the foregoing, Buyer shall pay within
fifteen business days of Seller's written request for payment all judgments,
damages, penalties, fines, assessments and other charges asserted against and
incurred by Seller with respect to any of the matters included in Buyer's
indemnity obligation hereunder.

          (D) In the event that any payment which Buyer is obliged to make to
Seller under this Agreement is not made within the fifteen day period set forth
in subsection (C), above, such payment shall bear interest at the rate of eight
percent per annum from the expiration date of such fifteen day period until the
date payment is actually received by Seller."

2.   All defined terms set forth herein without definition shall have the
meaning given such term in the Agreement.

3.   Except as set forth herein, all other terms and conditions of the Agreement
shall remain unchanged and continue in full force and effect.

                             AIR PRODUCTS AND CHEMICALS, INC.

                             By:___________________________

                             Title:________________________

                             PORT ARTHUR COKER COMPANY L.P.

                             By:___________________________

                             Title:________________________

                                      -2-

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