Document:

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                                                                Exhibit 4.19

                           SECOND AMENDED AND RESTATED

                            STOCKHOLDERS' AGREEMENT

                                    Between

                                CLARK USA, INC.

                                      and

                          OCCIDENTAL C.O.B. PARTNERS

                         Dated as of November 3, 1997

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                               Table of Contents

                                                                     Page

                                  ARTICLE I

                                 DEFINITIONS

         SECTION 1.01.   Certain Defined Terms.........................1

                                  ARTICLE II

                             CORPORATE GOVERNANCE

         SECTION 2.01.   Composition of the Board......................5
         SECTION 2.02.   Removal.......................................5
         SECTION 2.03.   Vacancies.....................................6

                                 ARTICLE III

                              TRANSFER OF SHARES

         SECTION 3.01.   General Restriction...........................6
         SECTION 3.02.   Legends.......................................6
         SECTION 3.03.   Certain Restrictions on Transfer..............7
         SECTION 3.04.   Right of First Refusal........................7
         SECTION 3.05.   Transferees to Execute Agreement.............10
         SECTION 3.06.   [RESERVED]...................................10
         SECTION 3.07.   RESERVED]....................................10
         SECTION 3.08.   Improper Sale or Encumbrance.................10

                                  ARTICLE IV

                            ADDITIONAL AGREEMENTS

         SECTION 4.01.   Registration Rights..........................11
         SECTION 4.02.   Incidental Registration......................12
         SECTION 4.03.   Registration Procedures......................13
         SECTION 4.04.   Preparation, Reasonable Investigation........16
         SECTION 4.05.   Indemnification..............................16
         SECTION 4.06.   Contribution.................................18
         SECTION 4.07.   Certain Information..........................19

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                                  ARTICLE V

                REPRESENTATIONS AND WARRANTIES OF THE PARTIES

         SECTION 5.01.   Representations and Warranties of Each
                           Party......................................20

                                  ARTICLE VI

                                MISCELLANEOUS

         SECTION 6.01.   Notices......................................21
         SECTION 6.02.   Public Announcements.........................21
         SECTION 6.03.   Headings.....................................22
         SECTION 6.04.   Severability.................................22
         SECTION 6.05.   Entire Agreement.............................22
         SECTION 6.06.   Assignment...................................22
         SECTION 6.07.   Parties in Interest..........................22
         SECTION 6.08.   Amendment....................................22
         SECTION 6.09.   Governing Law................................22
         SECTION 6.10.   Counterparts.................................23
         SECTION 6.11.   Specific Performance.........................23
         SECTION 6.12.   Termination..................................23

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          SECOND AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT, dated as of
November 3, 1997 (this "Agreement"), between CLARK USA, INC., a Delaware
corporation (the "Company"), and OCCIDENTAL C.O.B. PARTNERS, a Delaware
general partnership ("Oxy Partners" and, together with the Company, the
"Parties").

          WHEREAS, the Company and Oxy Partners have entered into a
Stockholders' Agreement dated as of December 1, 1995;

          WHEREAS, the Company and Oxy Partners have entered into an Amended
and Restated Stockholders' Agreement dated as of October 1, 1997 (the "First
Amended and Restated Stockholders' Agreement");

          WHEREAS, the Company and Oxy Partners desire to amend and restate
the First Amended and Restated Stockholders' Agreement as provided herein;

          NOW, THEREFORE. in consideration of the premises and the mutual
agreements and covenants hereinafter set forth, the Parties hereby agree as
follows:

                                   ARTICLE I

                                  DEFINITIONS

          SECTION 1.01. Certain Defined Terms. As used in this Agreement, the
following terms have the following meanings:

          "Accepting Party" has the meaning specified in Section 3.04(b).

          "affiliate" of a specified Person means a Person who, directly or
indirectly through one or more intermediaries, controls, is controlled by, or
is under common control with, such specified Person.

          "Agreement" means this Second Amended and Restated Stockholders'
Agreement.

          "beneficial owner" or "beneficially own" has the meaning given such
term in Rule l3d-3 under the Exchange Act as in effect on the date hereof,
provided that beneficial ownership under Rule 13d-3)(1)(i) shall be determined
based on whether a Person has a right to acquire beneficial ownership within
60 days or thereafter.

          "Board" means the Board of Directors of the Company.

          "Business Day" means any day that is not a Saturday, a Sunday or
other day on which banks are required or authorized by law to be closed in the
City of New York.

          "Capital Stock" means, with respect to any Person at any time, any
and all shares, interests, participation or other equivalents (however
designated, whether voting or non-

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voting) of capital stock, partnership interests (whether general or limited)
or equivalent ownership interests in or issued by such Person and any and all
warrants, options or other rights to purchase or acquire any of the foregoing.

          "Cash Equivalents" means (a) marketable direct obligations issued or
unconditionally guaranteed by the United States government or issued by any
agency thereof and backed by the full faith and credit of the United States,
in each case maturing within one year from the date of acquisition thereof,
(b) marketable direct obligations issued by any state of the United States or
any political subdivision of any such state or any public instrumentality
thereof maturing within one year from the date of acquisition thereof and, at
the time of acquisition, having the highest rating obtainable from any of
Standard & Poor's Corporation, Moody's Investors Service, Inc. or Duff &
Phelps Credit Rating Co. or (c) commercial paper maturing not more than one
year from the date of issuance thereof and, at the time of acquisition, having
the highest rating obtainable from either Standard & Poor's Corporation or
Moody's Investors Service, Inc.

          "Cause" has the meaning specified in Section 2.02(c).

          "Clark Capital Stock" means the Common Stock, Class A Common Stock,
Class D Common Stock, Class E Common Stock. Class F Common Stock and Preferred
Stock.

          "Class A Common Stock" means the Class A Common Stock, par value
$.01 per share, of the Company.

          "Class D Common Stock" means the Class D Common Stock, par value
$.01 per, share, of the Company.

          "Class E Common Stock" means the Class E Common Stock, par value
$.01 per share, of the Company.

          "Class F Common Stock" means the Class F Common Stock, par value
$.01 per share, of the Company.

          "Common Stock" means the Common Stock, par value $.01 per share, of
the Company.

          "Company" means Clark USA, Inc., a Delaware corporation. -------

          "control" (including the terms "controlled by" and "under common
control with"), with respect to the relationship between or among two or more
Persons, means the possession, directly or indirectly or as trustee or
executor of the power to direct or cause the direction of the affairs or
management of a Person, whether through the ownership of voting securities, as
trustee or executor, by contract or otherwise.

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          "Director" means a member of the Board.

          "Encumbrance" means any security interest, lien, claim, pledge,
limitation on voting rights, charge or other encumbrance of any nature
whatsoever.

          "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

          "Fully Diluted Shares" as of any date means the aggregate of (i) the
number of Shares issued and outstanding as of such date (other than Shares
held in the treasury of the Company or held by any Subsidiary of the Company)
and (ii) the number of Shares issuable as of such date upon (x) the exercise
of any then exercisable outstanding options, warrants or similar instruments
(other than any such instruments held by the Company or any Subsidiary of the
Company) and (y) the exercise of any then exercisable conversion or exchange
rights (other than any such rights held by the Company or any Subsidiary of
the Company).

          "Governmental Entity" means any administrative, governmental or
regulatory authority or body or any court or tribunal, domestic or foreign.

          "Laws" means any federal, state, local or foreign law, statute,
ordinance, rule, regulation, order, judgment or decree.

          "Marketable Securities" means securities that are (a) (i) securities
of or other interests in any Person that are traded on a national securities
exchange, reported on by NASDAQ or otherwise actively traded over-the-counter
or (ii) debt securities of a Person that has debt or equity securities that
are so traded or so reported on and in which a nationally recognized
securities firm has agreed to make a market, and (b) not subject to
restrictions on transfer as a result of any applicable contractual provisions
or the provisions of the Securities Act or any other applicable Law.

          "Minimum Sale Price" has the meaning specified in Section 3.04(d).

          "NASDAQ" means the National Association of Securities Dealers, Inc.
National Market System.

          "Nominee" has the meaning specified in Section 2.03)(a).

          "Notice of Acceptance" has the meaning specified in Section 3.04(b).

          "Offer" has the meaning specified in Section 3.04(a).

          "Offer Notice" has the meaning specified in Section 3.04(a).

          "Offer Notice Date" has the meaning specified in Section 3.04(b).

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          "Offer Period" has the meaning specified in Section 3.04(b).

          "Offer Price" has the meaning specified in Section 3.04(a).

          "Offered Shares" has the meaning specified in Section 3.04(a).

          "Other Stockholders" means all of the stockholders of the Company,
except for Oxy Partners, who shall agree to be bound by Article II hereof.

          "Oxy Director" has the meaning specified in Section 2.01.

          "Oxy Partners" means Occidental C.O.B. Partners, a Delaware general
partnership

         "Oxy Shares" means the Shares owned from time to time by Oxy Partners
and any Person to whom any of such shares are transferred from time to time.

         "Oxy Sub" means Occidental C.O.B. Co., Inc., a Delaware corporation.

         "Parties" means the Company and Oxy Partners.

         "Permitted Assignees" has the meaning specified in Section 3.04(b).

         "Permitted Transferee" means (a) the Company or any Subsidiary of the
Company, (b) Oxy Partners or (c) any affiliate of Oxy Partners; provided,
however, that any such affiliate shall cease to be a Permitted Transferee in
the event it shall cease to be an affiliate of Oxy Partners.

         "Person" means an individual, partnership, corporation (including a
business trust), limited liability company, joint stock company, trust,
unincorporated association, joint venture or other entity, or a government or
any political subdivision or agency thereof.

         "Preferred Stock" means the preferred stock, par value $0.01 per
share, of the Company.

         "Prospective Seller" has the meaning specified in Section 3.04(a).

         "Prospective Transferee" has the meaning specified in Section
3.05(a).

         "Public Offering" means an underwritten public offering of equity
securities of the Company pursuant to a registration statement that has been
declared effective by the SEC under the Securities Act, in which such equity
securities are widely distributed and after which such equity securities are
traded on a national securities exchange or reported on by NASDAQ.

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         "Recapitalization" means any stock split, dividend or combination, or
any recapitalization, merger, consolidation, exchange or other similar
reorganization.

         "Restricted Shares" means all Shares other than (a) Shares that have
been registered under a registration statement pursuant to the Securities Act,
(b) Shares with respect to which a Sale has been made in reliance on and in
accordance with Rule 144 and (c) Shares with respect to which the holder thereof
shall have delivered to the Company either (i) an opinion, in form and substance
reasonably satisfactory to the Company, of counsel, who shall be reasonably
satisfactory to the Company, or (ii) a "no action" letter from the staff of the
SEC, to the effect that subsequent transfers of such Shares may be effected
without registration under the Securities Act or compliance with Rule 144.

         "Rule 144" means Rule 144 (or any successor provision) under the
Securities Act.

         "Rule 144 Transaction" means any Sale of Oxy Shares made in reliance
upon Rule 144 (as in effect on the date hereof) that complies with paragraphs
(d), (e), (0 and (g) thereof (as in effect on the date hereof); provided that,
if, at the time of such Sale, the seller would otherwise be entitled to rely
upon paragraph (k) of Rule 144 in connection with such Sale, the number of Oxy
Shares included in such Sale, together with all other Sales of Oxy Shares by
such seller and its affiliates within any three-month period that includes the
date of such Sale, shall not exceed 1,500,000 Oxy Shares.

         "Sale" means any sale, assignment, transfer, distribution or other
disposition of Shares or of a participation therein, whether voluntarily or by
operation of law.

         "SEC" means the Securities and Exchange Commission, and any successor
commission or agency having similar powers.

         "Securities Act" means the Securities Act of 1933, as amended.

         "Share" means any share of Clark Capital Stock and any securities
issued in respect thereof, or in substitution therefor, in connection with any
Recapitalization.

         "Stockholder" means each Person (other than the Company) who shall be
a party to this Agreement, whether in connection with the execution and
delivery hereof as of the date hereof, pursuant to Section 3.05, or otherwise
(other than any Person who is a signatory to this Agreement solely for
purposes of being bound by Article 11), so long as such Person shall
beneficially own any Shares or any options, warrants or similar rights to
acquire Shares.

         "Subsidiary" means, with respect to any Person, any corporation,
partnership, limited liability company, joint venture, association or other
entity controlled by such Person directly or indirectly through one or more
intermediaries.

         "Third Party" means, with respect to any Stockholder, any other
Person other than a

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Permitted Transferee.

         "Trading Day" has the meaning specified in Section 3.04(g).

                                  ARTICLE II

                             CORPORATE GOVERNANCE

          SECTION 2.01. Composition of the Board. So long as Oxy Partners
and its affiliates own in the aggregate at least 10% of the Fully Diluted
Shares, Oxy Partners shall be entitled, to designate one Director for election
to the Board (the "Oxy Director"). Each Other Stockholder then entitled to
vote for the election of Directors to the Board shall vote all voting Shares
owned or held of record by such Person at any meeting of stockholders of the
Company, or execute a written consent with respect to all such Shares owned or
held of record by such Person, in favor of the election of the Oxy Director as
a Director. In the event Oxy Partners and its affiliates shall at any time not
own in the aggregate at least 10% of the Fully Diluted Shares, Oxy Partners
and such affiliates shall cause the Oxy Director to tender his or her written
resignation as a Director to the Secretary of the Company as soon as
practicable.

          SECTION 2.02. Removal. (a) Upon the written request of Oxy
Partners, each Other Stockholder shall vote all of his, her or its voting
Shares in favor of the removal of the Oxy Director. Each of the Other
Stockholders agrees that, if, at any time, he, she or it is then entitled to
vote for the removal of Directors, he, she or it will not vote any of his, her
or its voting Shares in favor of the removal of the Oxy Director unless such
removal shall be for Cause (as defined below) or Oxy Partners shall have
consented to or directed such removal in writing.

          (b) Upon the written request of an Other Stockholder that designated
a Director, each Stockholder shall vote all of his, her or its voting Shares
in favor of the removal of such Director. Each Stockholder agrees that, if, at
any time, he, she or it is then entitled to vote for the removal of Directors,
he, she or it will not vote any of his, her or its voting Shares in favor of
the removal of a Director designated by any of the Other Stockholders unless
the Other Stockholder that designated such Director to the Board shall have
consented to or directed such removal in writing.

          (c) Removal for "Cause" shall mean removal of a Director because of
such Director's (a) willful and continued failure to substantially perform his
or her duties as a Director, (b) willful conduct which is significantly
injurious to the Company, monetarily or otherwise, (c) conviction for, or
guilty plea to, a felony or a crime involving moral turpitude or (d) abuse of
illegal drugs or other controlled substances or habitual intoxication.

          SECTION 2.03. Vacancies. (a) If, as a result of death,
disability, retirement,

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resignation, removal (with or without Cause) or otherwise, there shall exist
or occur any vacancy on the Board due to the absence of a Director who shall
have been designated pursuant to Section 2.01, and the requirements of Section
2.01 shall remain satisfied in all respects, (i) Oxy Partners may designate,
in a writing executed by Oxy Partners, another individual to fill such vacancy
and to serve as a Director (the "Nominee") and (ii) each Other Stockholder
then entitled to vote for the election of Directors shall vote his, her or its
voting Shares at any meeting of stockholders of the Company, or execute a
written consent with respect to all such Shares, as the case may be, in favor
of the election of the Nominee as a Director.

          (b) If, as a result of death, disability, retirement, resignation,
removal (with or without Cause) or otherwise, there shall exist or occur any
vacancy on the Board due to the absence of a Director who shall have been
designated by one of the Other Stockholders, (i) the Other Stockholder who
designated such director may designate, in a writing executed by such Other
Stockholder, a Nominee and (ii) each Stockholder shall vote his, her or its
voting Shares at any meeting of stockholders of the Company, or execute a
written consent with respect to all such Shares, as the case may be, in favor
of the election of the Nominee as a Director.

                                 ARTICLE III

                              TRANSFER OF SHARES

          SECTION 3.01. General Restriction. No Stockholder shall, directly
or indirectly, make or solicit any Sale of, or create, incur, assume or suffer
to exist any Encumbrance with respect to, any Oxy Share beneficially owned by
such Stockholder, except in compliance with the Securities Act and the rules
and regulations thereunder and this Agreement.

          SECTION 3.02. Legends. (a) The Company shall affix to each
certificate evidencing Oxy Shares issued to Stockholders a legend in
substantially the following form:

          "THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN
          REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. NO
          REGISTRATION OF TRANSFER OF SUCH SECURITIES WILL BE MADE ON THE
          BOOKS OF THE ISSUER UNLESS SUCH TRANSFER IS MADE IN CONNECTION WITH
          AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT OR PURSUANT TO AN
          EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT OR SUCH ACT
          DOES NOT APPLY. THE SECURITIES EVIDENCED BY THIS CERTIFICATE ARE
          SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER AS SET FORTH IN AN
          AMENDED AND RESTATED STOCKHOLDERS' AGREEMENT DATED AS OF OCTOBER 1,
          1997, AS IT MAY BE AMENDED FROM TIME TO TIME, A COPY OF WHICH IS ON
          FILE AT THE PRINCIPAL EXECUTIVE OFFICES OF THE ISSUER. NO

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          REGISTRATION OF TRANSFER OF SUCH SECURITIES WILL BE MADE ON THE
          BOOKS OF THE ISSUER UNLESS AND UNTIL SUCH RESTRICTIONS SHALL HAVE
          BEEN COMPLIED WITH."

          (b) In the event that any Oxy Shares shall cease to be Restricted
Shares, the Company shall, upon the written request of the holder thereof,
issue to such holder a new certificate evidencing such Oxy Shares without the
first paragraph of the legend required by Section 3.02(a) endorsed thereon.

          (c) In the event that any Oxy Shares shall cease to be subject to
the restrictions on transfer set forth in this Agreement as provided in
Section 3.03(b), the Company shall, upon the written request of the holder
thereof, issue to such holder a new certificate evidencing such Oxy Shares
without the second paragraph of the legend required by Section 3.02(a)
endorsed thereon.

          SECTION 3.03. Certain Restrictions on Transfer. (a) Each Stockholder
agrees that it will not, directly or indirectly, make or solicit any Sale of,
or create, incur, assume or suffer to exist any Encumbrance (other than a
pledge or hypothecation of Oxy Shares to one or more bona fide financial
institutions and any foreclosure thereof, in each case subject to Section
3.05) with respect to, any Oxy Share beneficially owned by such Stockholder
other than (i) any Sale to a Permitted Transferee, (ii) any Sale for cash,
Cash Equivalents or Marketable Securities that is made in compliance with the
procedures, and subject to the limitations, set forth in Section 3.04, (iii)
any Sale pursuant to a Public Offering or (iv) any Sale in a Rule 144
Transaction. Notwithstanding the foregoing, except as otherwise expressly
provided in this Agreement, all Sales permitted by the foregoing clauses (i)
and (ii) shall be subject to, and shall not be made other than in compliance
with, the provisions of Sections 3.01, 3.02 and 3.05.

          (b) The restrictions on transfer set forth in this Agreement shall
cease to apply (i) as to any particular Oxy Shares at such time as such Oxy
Shares are sold pursuant to a Public Offering or a Rule 144 Transaction and
(ii) upon the termination of this Agreement.

          SECTION 3.04. Right of First Refusal. (a) If any Stockholder
receives from a Third Party dealing at arm's length a bona fide offer to
purchase for cash, Cash Equivalents or Marketable Securities (an "Offer") any
of the Oxy Shares owned or held by such Stockholder, and such Stockholder
intends to sell such Oxy Shares to such Third Party, such Stockholder (for
purposes of this Section 3.04, the "Prospective Seller") shall provide the
Company written notice of such Offer (an "Offer Notice"). The Offer Notice
shall identify the Third Party making the Offer, the number and class (or
classes) of Oxy Shares with respect to which the Prospective Seller has such
an Offer (the "Offered Shares"), the price per Offered Share at which a sale
is proposed to be made, determined in accordance with Section 3.04(g) ("Offer
Price"), the form of consideration in which the Offer Price is proposed to be
paid, and all other material terms and conditions of the Offer.

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          (b) The receipt of an Offer Notice by the Company from a Prospective
Seller (the date of such receipt being referred to herein as the "Offer Notice
Date") shall constitute an offer by such Prospective Seller to sell to the
Company and any assignee or assignees of the Company ("Permitted Assignees")
the Offered Shares at the Offer Price in cash. Such offer shall be irrevocable
during the Offer Period (as hereinafter defined). The Company and any
Permitted Assignees shall have the right to accept such offer as to any or all
of the Offered Shares by giving a written notice of acceptance (the "Notice of
Acceptance") to the Prospective Seller prior to the expiration of the Offer
Period (the Company or any Permitted Assignee so accepting such offer, an
"Accepting Party"); provided, however, that the Company and any Permitted
Assignees shall provide a single Notice of Acceptance to the Prospective
Seller and such Notice of Acceptance must accept the offer as to all of the
Offered Shares on the same terms and conditions as the Offer (other than as
expressly set forth herein). If the Company or any Permitted Assignee so
accepts the Prospective Seller's offer, such Person will purchase for cash
from the Prospective Seller, and the Prospective Seller will sell to such
Accepting Party, such number of Offered Shares as to which such Accepting
Party shall have accepted the Prospective Seller's offer (which must total, as
to all Accepting Parties, all of the Offered Shares). The price per Offered
Share to be paid by such Accepting Party shall be the Offer Price. The Notice
of Acceptance shall specify (i) each Accepting Party's acceptance of the
Prospective Seller's offer and (ii) the number of Offered Shares to be
purchased by each Accepting Party. "Offer Period" means (i) in the event the
Third Party making the Offer is engaged in the refining business, the twenty
Business Day period commencing on the date the Offer Notice is received by the
Company, or (ii) in all other cases, the ten Business Day period commencing on
the date the Offer Notice is received by the Company.

          (c) The consummation of such purchases by and sales to the Accepting
Parties shall take place on such date, not later than 90 days after receipt of
the Offer Notice by the Company (or such longer period as may be specified in
the Offer Notice), as the Accepting Parties and the Prospective Seller shall
select. Upon the consummation of such purchase and sale, the Prospective
Seller shall (i) deliver to the Accepting Party certificates evidencing the
Offered Shares purchased and sold duly endorsed in blank or accompanied by
written instruments of transfer in form satisfactory to such Accepting Party
duly executed by the Prospective Seller, and (ii) assign all its rights under
this Agreement with respect to the Offered Shares purchased and sold pursuant
to an instrument of assignment reasonably satisfactory to such Accepting
Party.

          (d) In the event that (i) the Company shall have received an Offer
Notice from a Prospective Seller but the Prospective Seller shall not have
received from the Company and its Permitted Assignees a Notice of Acceptance
with respect to all the Offered Shares prior to the expiration of the Offer
Period or (ii) an Accepting Party shall have given a Notice of Acceptance to
the Prospective Seller but such Accepting Party shall have failed to
consummate, other than as a result of the fault of the Prospective Seller, a
purchase of the Offered Shares with respect to which such Notice of Acceptance
was given within 90 days after receipt of the Offer Notice by the Company (or
such longer period as may be specified

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in the Offer Notice), such Prospective Seller shall have the right thereafter
to make a sale of the Offered Shares so long as all the Offered Shares that
are sold by the Prospective Seller (which number of Offered Shares shall be
not less than the number of Offered Shares specified in such Offer Notice) are
sold for cash, Cash Equivalents or Marketable Securities (i) within 180 days
after the date of receipt of such Offer Notice by the Company, (ii) at an
amount not less than the Minimum Sale Price (as hereinafter defined) and (iii)
to the Third Party that made the Offer. "Minimum Sale Price" means (x) if the
Prospective Seller's right to sell the Offered Shares results from the event
described in clause (i) of the preceding sentence, (A) an amount equal to 97
percent of the Offer Price set forth in the Offer Notice if such sale is
consummated within 30 days after the expiration of the Offer Period or (B) an
amount equal to 95 percent of the Offer Price set forth in the Offer Notice if
such sale is consummated thereafter, or (y) if the Prospective Seller's right
to sell the Offered Shares results from the event described in clause (ii) of
the preceding sentence, an amount equal to 90 percent of the Offer Price set
forth in the Offer Notice.

          (e) In the event (i) that the Company shall have received an Offer
Notice from a Prospective Seller, (ii) the Prospective Seller shall not have
received a Notice of Acceptance for all the Offered Shares prior to the
expiration of the Offer Period and (iii) such Prospective Seller shall not
have sold the remaining Offered Shares before the expiration of the 180-day
period in accordance with paragraph (d) above, then such Prospective Seller
shall not give another Offer Notice for a period of 120 days after the last
day of such 180-day period.

          (f) Anything in this Section 3.04 or in Section 3.03(a) to the
contrary notwithstanding, the provisions of this Section 3.04 shall not be
applicable to Sales of Clark Capital Stock described in clauses (i), (iii) and
(iv) of Section 3.03(a).

          (g) For the purpose of determining the Offer Price with respect to
an Offer that contemplates the payment of consideration in the form of Cash
Equivalents or Marketable Securities, the value of such Cash Equivalents or
Marketable Securities shall be determined as set forth in this Section
3.04(g). The value of Cash Equivalents shall be the fair market value of such
Cash Equivalents as of the Offer Notice Date as determined by a nationally
recognized investment banking firm selected by the Company and reasonably
acceptable to the Prospective Seller. The value of Marketable Securities shall
be, if such securities are listed or admitted to trading on a national
securities exchange, the average of the last sale prices for such securities
during the twenty consecutive Trading Days preceding the Offer Notice Date, as
reported in the principal consolidated transaction reporting system for
securities listed on the principal national securities exchange on which such
securities are listed or admitted to trading or, if such securities are not
listed or admitted to trading on any national securities exchange, the average
during the twenty consecutive Trading Days preceding the Offer Notice Date of
the last quoted price or, if not so quoted, the average of the high bid and
low asked prices in the over-the-counter market, as reported by NASDAQ or such
other system then in use, or, if on any such date such shares are not quoted
by any such organization, the average of the closing bid and asked prices as
furnished by a professional market maker making a market in such shares
selected by a majority of the Directors. If no market maker is making

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a market in such securities at such time, the fair value of such securities on
the Offer Notice Date shall be determined in good faith by a nationally
recognized investment banking firm selected by the Company and reasonably
acceptable to the Prospective Seller (the fees and expenses of which shall be
paid one-half by the Company and one-half by the Prospective Seller). If such
securities are not publicly held or not so listed or traded, the value of such
securities shall mean the fair value of such securities as of the Offer Notice
Date as determined in good faith by a nationally recognized investment banking
firm selected by the Company and reasonably acceptable to the Prospective
Seller (the fees and expenses of which shall be paid one-half by the Company
and one-half by the Prospective Seller), whose determination shall be
conclusive for all purposes. The term "Trading Day" shall mean, if such
securities are listed or admitted to trading on any national securities
exchange, a day on which the principal national securities exchange on which
such shares are listed or admitted to trading is open for the transaction of
business or, if such shares are not so listed or admitted, a Business Day.

          SECTION 3.05. Transferees to Execute Agreement. (a) Each Stockholder
agrees that it will not, directly or indirectly, make any Sale of, or create,
incur, assume or suffer to exist any Encumbrance with respect to, any Oxy
Shares beneficially owned by such Stockholder unless, contemporaneously with
or prior to the consummation of any such Sale or the creation, incurrence,
assumption or existence of such Encumbrance, the Person to whom such Sale is
proposed to be made or the Person in whose favor such Encumbrance is proposed
to be created, incurred, assumed or suffered to exist, in any case, (a
"Prospective Transferee"), executes and delivers to the Company its written
agreement, in form and substance reasonably satisfactory to the Company,
whereby such Prospective Transferee (i) confirms that, with respect to the Oxy
Shares that are the subject of such Sale or Encumbrance, it shall be deemed to
be a Stockholder for purposes of this Agreement and agrees to be bound by all
the terms of this Agreement, and (ii) represents and warrants that, upon the
consummation of such Sale or the creation, incurrence, assumption or existence
of such Encumbrance, such agreement is a legal, valid and binding obligation
of such Prospective Transferee enforceable against such Prospective Transferee
in accordance with its terms, subject to the effect of any applicable
bankruptcy, reorganization, insolvency, moratorium or similar laws affecting
creditors' rights generally and subject, as to enforceability, to the effect
of general principles of equity (regardless of whether such enforceability is
considered in a proceeding in equity or at law). Upon the execution and
delivery by such Prospective Transferee of the agreement referred to in the
preceding sentence, such Prospective Transferee shall be deemed a Stockholder
for purposes of this Agreement and shall have the rights and be subject to the
obligations of a Stockholder under this Agreement, in each case with respect
to the Oxy Shares beneficially owned by such Prospective Transferee or in
respect of which such Encumbrance shall have been created, incurred, assumed
or suffered to exist.

          (b) Anything in this Section 3.05 or in Section 3.03 to the contrary
notwithstanding, the provisions of this Section 3.05 will not be applicable to
any Sale of Oxy Shares pursuant to a Public Offering or a Rule 144
Transaction.

                                      11
<PAGE>

          SECTION 3.06. [RESERVED].

          SECTION 3.07. [RESERVED].

          SECTION 3.08. Improper Sale or Encumbrance. Any attempt not in
compliance with this Agreement to make any Sale of, or create, incur or assume
any Encumbrance with respect to, any Oxy Shares shall be null and void and of
no force and effect, the purported transferee shall have no rights or
privileges in or with respect to the Company, and the Company shall not give
any effect in the Company's stock records to such attempted Sale or
Encumbrance.

                                  ARTICLE IV

                             ADDITIONAL AGREEMENTS

          SECTION 4.01. Registration Rights. (a) If the Company is a Public
Company, upon the written request of Oxy Partners or any Permitted Transferee
of Oxy Partners requesting that the Company effect the registration under the
Securities Act of all or part of the Oxy Shares held by such Person and
specifying the intended method of disposition thereof, the Company shall
promptly give written notice of such requested registration to all other
holders of Shares, and thereupon will, as expeditiously as possible, use its
commercially reasonable efforts to effect the registration under the
Securities Act of the Oxy Shares that the Company has been so requested to
register by such holder, provided that (i) the Company shall be obligated to
register Oxy Shares pursuant to this Section 4.01(a) on only one occasion,
(ii) the Company shall not be obligated to file a registration statement
relating to any registration request under this Section 4.01(a) if with
respect thereto the managing underwriter, the SEC, the Securities Act or the
rules and regulations thereunder, or the form on which the registration
statement is to be filed, would require the conduct of an audit other than the
regular audit conducted by the Company at the end of its fiscal year, in which
case the filing may be delayed until the completion of such regular audit
(unless the holders of the Oxy Shares to be registered agree to pay the
expenses of the Company in connection with such an audit other than the
regular audit); provided, however, that the work required to be performed to
enable the Company's auditors to issue their consent or a "cold comfort"
letter shall not be deemed to be an audit, and (iii) if the Company, in its
sole discretion, determines that the filing of a registration statement in the
near future pursuant to this Section 4.01 would interfere with any financing,
acquisition, corporate reorganization or other similar transaction involving
the Company or any Subsidiary of the Company or that such registration would
require disclosure of non-public information that the Company deems advisable
not to disclose, then the Company's obligation to file a registration
statement shall be deferred for a period not to exceed 180 days.

          (b) If any registration requested pursuant to this Section 4.01 that
is proposed by the Company to be effected by the filing of a registration
statement on Form S-3) (or any successor or similar short-form registration
statement) shall be in connection with an

                                      12
<PAGE>

underwritten public offering, and if the managing underwriter shall advise the
Company in writing that, in its opinion, the use of another form of
registration statement is of material importance to the success of such
proposed offering, then such registration shall be effected on such other
form.

          (c) A registration requested pursuant to this Section 4.01 shall not
be deemed to have been effected unless it has become effective and, even in
that event, such registration shall not be deemed to have been effected if
within 180 days after it has become effective, the offering of Oxy Shares
pursuant to such registration is interfered with by any stop order, injunction
or other order or requirement of the SEC or other governmental agency or court
(unless such stop order, injunction or other order or requirement arises out
of or in connection with an action or failure to act or misstatement or
omission by the Person requesting such registration).

          (d) If a requested registration pursuant to this Section 4.01
involves an underwritten offering, Oxy Partners shall have the right to select
the lead underwriter or underwriters and managers to administer the offering,
which shall be nationally recognized investment banking firms reasonably
satisfactory to the Company, and the Company shall have the right to select a
co-manager for the offering.

          (e) If a requested registration pursuant to this Section 4.01
involves an underwritten offering and the managing underwriter advises the
Company in writing that, in its opinion, the number of securities requested to
be included in such registration (including securities issued or to be issued
by the Company that are not Oxy Shares) should be limited because the
inclusion of all of such securities is likely to adversely impact the purchase
price obtained for such securities, the Company shall include in such
registration securities in the following order of priority: first, Oxy Shares
requested to be Included in such registration pursuant to this Section 4.01
and second, any other securities of the Company.

          (f) For purposes of this Agreement, the Company shall be deemed to
be a "Public Company" if, as of any date of determination, any Shares shall
have been sold in a Public Offering and any Shares are registered under the
Exchange Act.

          SECTION 4.02. Incidental Registration. If the Company at any time
proposes to register any Shares under the Securities Act for Sale in a Public
Offering, whether or not for its own account, on a form and in a manner that
would permit registration of Oxy Shares under the Securities Act for Sale in
such Public Offering, the Company shall give prompt written notice to all
holders of Oxy Shares of its intention to do so, specifying the form and
manner and the other relevant facts involved in such proposed registration
(including, without limitations the identity of the managing underwriter).
Upon the written request of any holder of Oxy Shares delivered to the Company
within ten days after such notice shall have been given to such holder (which
request shall specify the number of Oxy Shares intended to be disposed of by
such holder and the intended method of disposition thereof), the Company shall
use its commercially reasonable efforts to effect the registration under the
Securities Act,

                                      13
<PAGE>

as expeditiously as is reasonable, of all Oxy Shares that the Company has been
so requested to register by the holders of Oxy Shares, to the extent requisite
to permit the Sale of the Oxy Shares to be so registered in such Public
Offering; provided, however, that:

          (a) if, at any time after giving such written notice of its
intention to register any of such Shares proposed to be registered by the
Company and prior to the effective date of the registration statement filed in
connection with such registration, the Company shall determine for any reason
not to register such Shares, the Company may, at its election, give written
notice of such determination to each holder of Oxy Shares that has requested
to register Oxy Shares and thereupon the Company shall be relieved of its
obligation to register any Oxy Shares in connection with such registration;

          (b) if the managing underwriter of such Public Offering shall advise
the Company that, in its judgment, the number of Shares proposed to be
included in such Public Offering should be limited because the inclusion of
Oxy Shares is likely to adversely impact the purchase price obtained for the
Shares initially proposed to be included in such Public Offering by the
Company (whether or not for its own account), then the Company shall promptly
advise each holder of such Oxy Shares thereof and may require, by written
notice to each such holder accompanying such advice, that, to the extent
necessary to meet such limitation, the number of Oxy Shares to be included in
such registration shall be reduced, and all holders of Oxy Shares proposing to
sell Shares in such Public Offering shall share pro rata in the number of
Shares to be excluded from such offering, such sharing to be based on the
respective numbers of Shares as to which they have requested registration; and

          (c) the Company shall not be obligated to effect any registration of
Oxy Shares under this Section 4.02 that is incidental to the registration of
any of its Shares or other securities in connection with any merger,
acquisition, exchange offer, dividend reinvestment plan or stock option, stock
purchase, savings or other employee benefit plan.

          SECTION 4.03. Registration Procedures. If and whenever the Company
is required to use its commercially reasonable efforts to effect the
registration of any Oxy Shares as provided in Section 4.01 or 4.02, the
Company will as expeditiously as is reasonably practicable:

          (i) prepare and file with the SEC on any appropriate form a
registration statement with respect to such Oxy Shares and use its
commercially reasonable efforts to cause such registration statement to become
effective;

          (ii) prepare and file with the SEC such amendments (including
post-effective amendments) and supplements to such registration statement and
the prospectus used in connection therewith as may be necessary to keep such
registration statement effective and to comply with the provisions of the
Securities Act and the rules and regulations thereunder with respect to the
disposition of all Oxy Shares and other securities covered by such
registration statement until the earlier of (A) such time as all such Oxy
Shares and other securities have

                                      14
<PAGE>

been disposed of in accordance with the intended methods of disposition by the
seller or sellers thereof set forth in such registration statement and (B) the
expiration of 180 days from the date such registration statement first becomes
effective (or such other period as may be agreed upon by the Company and the
managing underwriter);

          (iii) furnish to each seller of such Oxy Shares Such number of
conformed copies of such registration statement and of each such amendment and
supplement thereto (in each case including all exhibits), such number of
copies of the prospectus included in such registration statement (including
each preliminary prospectus and any summary prospectus), in conformity with
the requirements of the Securities Act and the rules and regulations
thereunder, such documents incorporated by reference in such registration
statement or prospectus, and such other documents, as such seller may
reasonably request in order to facilitate the sale or disposition of such Oxy
Shares;

          (iv) use its commercially reasonable efforts to register or qualify
all Oxy Shares covered by such registration statement under such other
securities or "blue sky" laws of such U.S. jurisdictions as each seller shall
reasonably request, and do any and all other acts and things that may be
necessary to enable such seller to consummate the disposition in such
jurisdictions of its Oxy Shares covered by such registration statement, except
that the Company shall not for any such purpose be required to qualify
generally to do business as a foreign corporation in any jurisdiction wherein
it is not so qualified, or to subject itself to taxation in respect of doing
business in any such jurisdiction, or to consent to general service of process
in any such jurisdiction;

          (v) enter into such customary agreements (including an underwriting.
agreement in customary form), which may include indemnification provisions in
favor of underwriters and other persons in addition to, or in substitution for
the provisions of Section 4.06, and take such other actions as sellers of a
majority of Oxy Shares or the underwriters, if any, reasonably request in
order to expedite or facilitate the disposition of such Oxy Shares;

          (vi) furnish to each seller of Oxy Shares (x) a signed counterpart,
addressed to such seller, of any opinion of counsel for the Company, dated the
date of the closing under the underwriting agreement with respect to such
Public Offering, and (Y) a signed counterpart, if requested by such seller,
managing underwriter or other seller of securities included in such
registration, addressed to such seller, of any "cold comfort" letter signed by
the independent public accountants in customary form and covering matters of
the type customarily covered by "cold comfort" letters as the managing
underwriter or seller of such Oxy Shares shall reasonably request (provided
that Oxy Shares constitute at least 25% of the securities covered by such
registration statement, unless such a "cold comfort" letter or letters are
provided to the Company, managing underwriter or other selling holders in
connection with such registration);

          (vii) immediately notify each seller of Oxy Shares covered by such
registration statement at any time when a prospectus relating thereto is
required to be delivered under the

                                      15
<PAGE>

Securities Act and the rules and regulations thereunder, of the happening of
any event as a result of which the prospectus included in such registration
statement, as then in effect, includes an untrue statement of a material fact
or omits to state any material fact required to be stated therein or necessary
to make the statements therein not misleading in the light of the
circumstances then existing or if it is necessary to amend or supplement such
prospectus to comply with law, and at the request of any such seller prepare
and furnish to such seller a reasonable number of copies of a supplement to or
an amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such Oxy Shares or other securities, such
prospectus shall not include an untrue statement of a material fact or omit to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing and shall otherwise comply in all material respects with law and so
that such prospectus, as amended or supplemented, will comply with law;

          (viii) otherwise use its commercially reasonable efforts to comply
with all applicable rules and regulations of the SEC, and make available to
its security holders, as soon as reasonably practicable, an earnings statement
which shall satisfy the provisions of Section II(a) of the Securities Act
and the rules and regulations thereunder;

          (ix) use its commercially reasonable efforts to list such Oxy Shares
on each securities exchange or quotation system on which Shares are then
listed or quoted, if such Oxy Shares are not already so listed or quoted and
if such listing is then permitted under the rules of such exchange or
quotation system, and provide a transfer agent and registrar for such Oxy
Shares not later than the effective date of such registration statement;

          (x) cooperate with the holders of Oxy Shares covered by the
registration statement and the managing underwriter or agent, if any, to
facilitate the timely preparation and delivery of certificates (not bearing
any restrictive legends) representing securities to be sold under the
registration statement, and enable such securities to be in such denominations
and registered in such names as the managing underwriter or agent, if any, or
such holders may request;

          (xi) notify counsel for the holders of Oxy Shares included in such
registration statement and the managing underwriter or agent, immediately (i)
when the registration statement, or any post-effective amendment to the
registration statement, shall have become effective, or any supplement to the
prospectus or any amendment to the prospectus shall have been filed, (ii) of the
receipt of any comments from the SEC, (iii) of any request of the SEC to amend
the registration statement or amend or supplement the prospectus or for
additional information, and (iv) of the issuance by the SEC of any stop order
suspending the effectiveness of the registration statement or of any order
preventing or suspending the use of any preliminary prospectus, or of the
suspension of the qualification of the registration statement for offering or
sale in any jurisdiction, or of the institution or threatening of any
proceedings for any of such purposes;

                                      16
<PAGE>

          (xii) make every commercially reasonable effort to prevent the
issuance of any stop order suspending the effectiveness of the registration
statement or of any order preventing or suspending the use of any preliminary
prospectus and, if any such order is issued, to obtain the withdrawal of any
such order at the earliest possible moment;

          (xiii) if requested by the managing underwriter or agent or any
holder of Oxy Shares covered by the registration statement, promptly
incorporate in a prospectus supplement or post-effective amendment such
information as the managing underwriter or agent or such holder reasonably
requests to be included therein, including, without limitation, with respect
to the number of Oxy Shares being sold by such holder to such underwriter or
agent, the purchase price being paid therefor by such underwriter or agent and
with respect to any other terms of the underwritten offering of the Oxy Shares
to be sold in such offering; and make all required filings of such prospectus
supplement or post-effective amendment as soon as practicable after being
notified of the matters incorporated in such prospectus supplement or
post-effective amendment;

          (xiv) cooperate with each seller of Oxy Shares and each underwriter
or agent participating in the disposition of such Oxy Shares and their
respective counsel in connection with any filings required to be made with the
National Association of Securities Dealers, Inc.; and

          (xv) issue to any underwriter to which any holder of Oxy Shares may
sell such Oxy Shares in connection with any such registration (and to any
direct or indirect transferee of any such underwriter) certificates evidencing
Oxy Shares without the legends described in Section 3.02(a).

The Company may require each seller of Oxy Shares as to which any registration
is being effected to furnish the Company with such information regarding such
seller and the distribution of such Oxy Shares as the Company may from time to
time reasonably request in writing in connection therewith.

          (b) Each holder of Oxy Shares agrees, if so required by the managing
underwriters, not to effect any public sale or distribution (including any
sale pursuant to Rule 144) of Shares (other than as part of such Public
Offering) within 7 days prior to the anticipated effective date of the
registration statement with respect to such underwritten public offering or
180 days after the effective date of such registration statement.

          (c) The Company agrees, if so required by the managing underwriters in
connection with such Public Offering of Oxy Shares pursuant to Section 4.01 or
Section 4.02, not to effect any public sale or distribution of any of its equity
securities or securities convertible into or exchangeable or exercisable for any
of such equity securities within the seven days prior to the anticipated
effective date of the registration statement with respect to such Public
Offering or 180 days after the effective date of such registration statement,
except as part of such Public Offering or except in connection with a dividend
reinvestment plan, a

                                      17
<PAGE>

stock option, stock purchase, savings or other employee benefit plan, or an
acquisition, merger or exchange offer.

          SECTION 4.04. Preparation, Reasonable Investigation. In connection
with the preparation and filing of a registration statement pursuant to
Section 4.01 or Section 4.02, the Company will give the holders of Oxy Shares
on whose behalf such Oxy Shares are to be so registered and their
underwriters, if any, and their respective counsel, accountants and other
agents the opportunity to participate in the preparation of such registration
statement, each prospectus included therein or filed with the SEC, and each
amendment thereof or supplement thereto, and will give each of them such
access to its books and records and such opportunities to discuss the business
of the Company with its officers and the independent public accountants who
have issued a report on its financial statements as shall be necessary, in the
opinion of such holders and such underwriters or their respective counsel, to
conduct a reasonable investigation within the meaning of the Securities Act.

          SECTION 4.05. Indemnification. (a) In the event of any registration
of Oxy Shares pursuant to Section 4.01 or Section 4.02, the Company shall
indemnify and hold harmless the seller of any Oxy Shares covered by such
registration statement, its directors and officers, general and limited
partners (and directors and officers thereof and, if such seller is a
portfolio or investment fund, its investment advisors), each other Person who
participates as an underwriter in the Public Offering of such Oxy Shares, each
officer and director of each such underwriter, and each other Person, if any,
who controls such seller or any such underwriter within the meaning of Section
15 of the Securities Act, against any losses, claims, damages, liabilities and
expenses (including, without limitation, reasonable attorneys' fees and any
and all reasonable expenses incurred in investigating, preparing or defending
against any litigation, commenced or threatened, or any claim, and any and all
amounts paid in settlement of any such claim or litigation) to which such
seller or any such director or officer or participating or controlling Person
may become subject under the Securities Act, the Exchange Act, the rules and
regulations thereunder or otherwise, insofar as such losses, claims, damages,
liabilities or expenses (or actions or proceedings in respect thereof) arise
out of or are based upon (i) any untrue statement or alleged untrue statement
of any material fact contained in the registration statement under which such
Oxy Shares were registered under the Securities Act, any preliminary
prospectus, final prospectus or summary prospectus included therein, or any
amendment or supplement thereto, or any document incorporated by reference
therein, (ii) any omission or alleged omission to state therein a material
fact required to be stated therein or necessary to make the statements therein
not misleading, or (iii) any failure by the Company to comply with the
requirements of the Securities Act, the Exchange Act, any state securities
laws or any rule or regulation promulgated under any of the foregoing, and the
Company will reimburse such seller, and each such director, officer,
underwriter and controlling Person for any legal or any other expenses
reasonably incurred by them in connection with investigating or defending any
such loss, claim, liability, action or proceeding; provided, however, that the
Company shall not be liable in any such case to the extent that any such loss,
claim, damage, liability (or action or proceeding in respect thereof) or
expense arises out of or is based upon (i) an untrue statement or alleged
untrue statement or omission or alleged omission made in

                                      18
<PAGE>

such registration statement, any such preliminary prospectus, final
prospectus, summary prospectus, amendment or supplement in reliance upon and
in conformity with written information furnished to the Company for use in the
preparation thereof by such seller or underwriter, as the case may be, or (ii)
an untrue statement or alleged untrue statement or omission or alleged
omission made in any preliminary prospectus but notified to such seller and
underwriter prior to any sale of Oxy Shares and subsequently corrected by the
Company in any final prospectus, amendment or supplement made available to
Such seller or underwriter but which final prospectus, amendment or supplement
was not used by such seller or underwriter in the sale of Oxy Shares that gave
rise to such loss, claim, damage, liability (or action or proceeding in
respect thereof) or expense. Such indemnity shall remain in full force and
effect regardless of any investigation made by or on behalf of such seller or
any such director, officer, underwriter or controlling Person and shall
survive the transfer of such Oxy Shares by such seller.

          (b) The Company may require, as a condition to including any Oxy
Shares in any registration statement filed pursuant to Section 4.01 or Section
4.02, that the Company shall have received an undertaking satisfactory to it
from (i) the prospective seller of such Oxy Shares, to indemnify and hold
harmless the Company, each underwriter of such Shares, each officer and
director of each such underwriter and each other Person, if any, who controls
the Company or any such underwriter within the meaning of Section 15 of the
Securities Act, and (ii) each underwriter of such Oxy Shares, to indemnify and
hold harmless the Company, each officer and director of the Company, each
prospective seller, each officer and director of each prospective seller and
each other Person, if any, who controls the Company or any such prospective
seller within the meaning of Section 15 of the Securities Act, against any
losses, claims, damages, liabilities and expenses (including, without
limitation, reasonable attorneys' fees and any and all reasonable expenses
incurred in investigating, preparing or defending against any litigation,
commenced or threatened, or any claim, and any and all amounts paid in
settlement of any such claim or litigation) to which such Person or any such
director or officer or participating or controlling Person may become subject
under the Securities Act, the Exchange Act, the rules and regulations
thereunder or otherwise, insofar as such losses, claims, damages, liabilities
or expenses (or actions or proceedings in respect thereof) arise out of or are
based upon (i) any untrue statement or alleged untrue statement of any
material fact contained in the registration statement under which such Oxy
Shares were registered under the Securities Act, any preliminary prospectus,
final prospectus or summary prospectus included therein, or any amendment or
supplement thereto, or any document incorporated by reference therein, in
reliance upon and in conformity with written information furnished to the
Company for use in the preparation thereof by the party from whom
indemnification is sought hereunder, (ii) any omission or alleged omission to
state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading in reliance upon and in conformity
with written information furnished to the Company for use in the preparation
thereof by the party from whom indemnification is sought hereunder, or (iii)
any failure by the party from whom indemnification is sought to comply with
the requirements of the Securities Act, the Exchange Act, any state securities
laws or any rule or regulation promulgated under any of the foregoing and the
indemnifying party will reimburse each

                                      19
<PAGE>

indemnified party, and each such director, officer, underwriter and
controlling Person for any legal or any other expenses reasonably incurred by
them in connection with investigating or defending any such loss, claim,
liability, action or proceeding. Such indemnity shall remain in full force and
effect regardless of any investigation made by or on behalf of the Company or
any such director, officer or controlling Person and shall survive the
transfer of such Oxy Shares by such seller.

          (c) Promptly after receipt by an indemnified party of notice of the
commencement of any action or proceeding (including any governmental
investigation) involving a claim referred to in Section 4.05(a) or (b), such
indemnified party will, if a claim in respect thereof is to be made against an
indemnifying party, give written notice to the latter of the commencement of
such action; provided, however, that the failure of any indemnified party to
give notice as provided herein shall not relieve the indemnifying party of its
obligations under the preceding provisions of this Section 4.05, except to the
extent that the indemnifying party is actually prejudiced by such failure to
give notice. In case any such action is brought against an indemnified party,
unless in such indemnified party's reasonable judgment a conflict of interest
between such indemnified and indemnifying parties may exist in respect of such
claim (in which case, the indemnifying party shall not be liable for the fees
and expenses of more than one counsel for all sellers of Oxy Shares and more
than one counsel for the underwriters in connection with any one action or
separate but similar or related actions), the indemnifying party will be
entitled to participate in and to assume the defense thereof, jointly with any
other indemnifying party similarly notified, to the extent that it may wish
with counsel reasonably satisfactory to such indemnified party, and after
notice from the indemnifying party to such indemnified party of its election
so to assume the defense thereof, the indemnifying party will not be liable to
such indemnified party for any legal or other expenses subsequently incurred
by the latter in connection with the defense thereof. No indemnifying party
will consent to entry of any judgment or enter into any settlement which does
not include as an unconditional term thereof, the giving by the claimant or
plaintiff to such indemnified party of a release, in form and substance
reasonably satisfactory to such indemnified party, from all liability in
respect to such claim or litigation. No indemnified party will consent to the
entry of any judgment or enter into any settlement with respect to such claim
or litigation without the written consent of the indemnifying party.

          SECTION 4.06. Contribution. (a) If the indemnification provided for
in Section 4.05 is unavailable to the indemnified parties in respect of any
losses, claims, damages or liabilities referred to therein, then each
indemnifying party and the Company shall contribute to the amounts paid or
payable by such indemnified parties as a result of such losses, claims,
damages or liabilities (i) as between the Company and the holders of Oxy
Shares covered by a registration statement, on the one hand, and the
underwriters, on the other, in such proportion as is appropriate to reflect
the relative benefits received by the Company and such holders, on the one
hand, and the underwriters, on the other, from the Public Offering of the Oxy
Shares, or if such allocation is not permitted by applicable law, in such
proportion as is appropriate to reflect not only the relative benefits but
also the relative fault of the Company and such holders, on the one hand, and
of the underwriters, on the other, in connection with

                                      20
<PAGE>

the statements or omissions that resulted in such losses, claims, damages or
liabilities, as well as any other relevant equitable considerations, and (ii)
as between the Company, on the one hand, and each holder of Oxy Shares covered
by a registration statement, on the other, in such proportion as is
appropriate to reflect the relative fault of the Company and of each such
holder in connection with such statements or omissions, as well as any other
relevant equitable considerations. The relative benefits received by the
Company and such holders, on the one hand, and the underwriters, on the other,
shall be deemed to be in the same proportion as the total proceeds from the
Public Offering (net of underwriting discounts and commissions but before
deducting expenses) received by the Company and such holders bear to the total
underwriting discounts and commissions received by the underwriters. The
relative fault of the Company and such holders, on the one hand, and of the
underwriters, on the other, shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or
the omission or alleged omission to state a material fact relates to
information supplied by the Company and such holders or by the underwriters.
The relative fault of the Company, on the one hand, and of each such holder,
on the other, shall be determined by reference to, among other things, whether
the untrue or alleged untrue statement of a material fact relates to
information supplied by such party, and the parties' relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission.

          (b) The Company and the holders of Oxy Shares agree that it would
not be just and equitable if contribution pursuant to this Section 4.06 were
determined by pro rata allocation (even if the underwriters were treated as
one entity for such purpose) or by any other method of allocation that does
not take account of the equitable considerations referred to in the next
preceding paragraph. The amount paid or payable by an indemnified party as a
result of the losses, claims, damages or liabilities referred to in the next
preceding paragraph shall be deemed to include, subject to the limitations set
forth above, any legal or other expenses reasonably incurred by such
indemnified party in connection with investigating or defending any such
action or claim. Notwithstanding the provisions of this Section 4.06, no
underwriter shall be required to contribute any amount in excess of the amount
by which the total price at which the Oxy Shares underwritten by it and
distributed to the public were offered to the public pursuant to such Public
Offering exceeds the amount of any damages that such underwriter has otherwise
been required to pay by reason of such untrue or alleged untrue statement or
omission or alleged omission, and no holder of Oxy Shares shall be required to
contribute any amount in excess of the amount by which the total price at
which the Oxy Shares of such holder were offered to the public pursuant to
such Public Offering exceeds the amount of any damages that such holder has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission. No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any person who was not guilty of such
fraudulent misrepresentation. Each holder's obligation to contribute pursuant
to this Section 4.06 is several in the proportion that the proceeds of the
Public Offering received by such holder bears to the total proceeds of the
Public Offering received by all the holders of Oxy Shares and not joint.

                                      21
<PAGE>

          SECTION 4.07. Certain Information. In the event that and so long as
the Company shall be a Public Company, it shall file all reports and other
information required to be filed by Section 13 or 15(d) under the Exchange
Act, as the case may be, within the respective time periods prescribed thereby
for the filing of such reports and other information, as shall be necessary in
order that the conditions to the availability of Rule 144 in connection with
any Sale of Oxy Shares by a Stockholder shall be met.

                                  ARTICLE V

                 REPRESENTATIONS AND WARRANTIES OF THE PARTIES

          SECTION 5.01. Representations and Warranties of Each Party. Each
Party hereby makes the following representations and warranties to the other
Parties:

                    (a) Organization and Qualification. Such entity is a
          corporation or a general partnership duly organized, validly
          existing and in good standing under the laws of its jurisdiction of
          organization.

                    (b) Authority. Such entity has all requisite corporate or
          partnership power and authority to execute and deliver this
          Agreement, to perform its obligations hereunder and to consummate
          the transactions contemplated hereby. The execution and delivery of
          this Agreement by such entity and the consummation by it of the
          transactions contemplated hereby have been duly and validly
          authorized by all necessary corporate or partnership action and no
          other proceedings on the part of such entity are necessary to
          authorize this Agreement or to consummate the transactions
          contemplated hereby. This Agreement has been duly and validly
          executed and delivered by such entity and, assuming the due
          authorization, execution and delivery by the other parties thereto,
          constitutes a legal, valid and binding obligation of such entity,
          enforceable against such entity in accordance with its terms.

                    (c) No Conflict; Required Filings and Consents. (i) The
          execution of and delivery of this Agreement by such entity do not,
          and the performance this Agreement by such entity will not, (A)
          conflict with or violate the Certificate of Incorporation, By-Laws
          or similar organizational documents of such entity, (B) conflict
          with or violate any Laws applicable to such entity or by which any
          of its properties or assets is bound or (C) result in any breach of
          or constitute a default (or an event that with notice or lapse of
          time or both would become a default) under, or give to others any
          rights of termination, amendment, acceleration or cancellation of,
          or result in the creation of an Encumbrance on any of the properties
          or assets of such entity pursuant to, any note, bond, mortgage,
          indenture, contract, agreement, lease, license, permit, franchise or
          other instrument or obligation to which such entity is a party or by
          which such entity or any of its properties is bound, except in any
          case for such conflicts,

                                      22
<PAGE>

          violations, breaches, defaults or other effects which would not
          prevent or materially delay the performance by such entity of its
          obligations hereunder.

                    (ii) The execution and delivery of this Agreement by such
          entity do not, and the performance of this Agreement by such entity
          will not, require any consent, approval, authorization or permit of,
          or filing with or notification to, any Governmental Entity.

                                  ARTICLE VI

                                 MISCELLANEOUS

          SECTION 6.01. Notices. All notices, requests, claims, demands and
other communications hereunder shall be in writing and shall be given (and
shall be deemed to have been duly given upon receipt) by delivery in person,
by telecopy or by registered or certified mail (postage prepaid, return
receipt requested) to the respective parties at the following addresses (or at
such other address for a party as shall be specified in a notice given in
accordance with this Section 6.01):

          (a) If to the Company:

              Clark USA, Inc.
              8182 Maryland Avenue
              St. Louis, Missouri 63105-3721
              Telecopier No.: (314) 854-1599
              Attention:   Maura Clark, Executive Vice President, Corporate
                           Development and Chief Financial Officer

              With copies to:

              Mayer, Brown & Platt
              190 South LaSalle Street
              Chicago, Illinois 60603-3441
              Telecopier No.: (312) 701-7711
              Attention:   Richard S. Millard, Esq.

          (b) If to Oxy Partners:

              c/o Occidental Petroleum Corporation
              10889 Wilshire Blvd.
              Los Angeles, California 90024
              Telecopier No.: (310) 443-6812
              Attention:   Stephen I. Chazen

                                      23
<PAGE>

                           Executive Vice President, Corporate Development

              With a copy to:

              Occidental Petroleum Corporation
              10889 Wilshire Blvd.
              Los Angeles, California 90024
              Telecopier No.: (310) 443-6333
              Attention:   General Counsel

          SECTION 6.02. Public Announcements. The Parties shall consult with
each other before issuing any press release or otherwise making any public
statements with respect to this Agreement and, except as may be required by
Law or any listing agreement with any securities exchange, shall not issue any
such press release or make any such public statement without the consent of
the other parties.

          SECTION 6.03. Headings. The descriptive headings contained in
this Agreement are for reference purposes only and shall not affect in any way
the meaning or interpretation of this Agreement.

          SECTION 6.04. Severability. If any term or other provision of this
Agreement is invalid, illegal or incapable of being enforced by any rule of
Law or public policy, all other conditions and provisions of this Agreement
shall nevertheless remain in full force and effect so long as the economic or
legal substance of the transactions contemplated hereby is not affected in any
manner materially adverse to any Party. Upon such determination that any term
or other provision is invalid, illegal or incapable of being enforced, the
Parties shall negotiate in good faith to modify this Agreement so as to effect
the original intent of the Parties as closely as possible in an acceptable
manner to the end that the transactions contemplated hereby are fulfilled to
the extent possible.

          SECTION 6.05. Entire Agreement. This Agreement constitutes the
entire agreement among the Parties and supersedes all prior agreements and
undertakings, both written and oral, among the Parties, or any of them, with
respect to the subject matter hereof.

          SECTION 6.06. Assignment. Except as otherwise provided herein, this
Agreement shall be binding upon and shall inure to the benefit of the Parties
and their respective successors and permitted assigns; provided, however, that
this Agreement shall not inure to the benefit of any Prospective Transferee
unless such Prospective Transferee shall have complied with the terms of
Section 3.05. No Stockholder may assign any of its rights hereunder to any
Person other than a transferee that has complied with the requirements of
Section 3.05 in all respects.

          SECTION 6.07. Parties in Interest. Nothing in this Agreement,
express or implied, is intended to or shall confer upon any Person other than
the Parties and their respective

                                      24
<PAGE>

successors and assigns any right, benefit or remedy of any nature whatsoever
under or by reason of this Agreement.

          SECTION 6.08. Amendment. (a) Any term of this Agreement may be
amended and the observance of any such term may be waived (either generally or
in a particular instance and either retroactively or prospectively) only with
the written consent of the Company and Oxy Partners.

          (b) No failure or delay by any party in exercising any right, power
or privilege under this Agreement shall operate as a waiver thereof nor shall
any single or partial exercise thereof preclude any other or further exercise
thereof or the exercise of any other right, power or privilege. The rights and
remedies herein provided shall be cumulative and not exclusive of any rights
or remedies provided by law.

          SECTION 6.09. Governing Law. This Agreement shall be governed by,
and construed in accordance with, the laws of the State of New York applicable
to contracts executed in and to be performed entirely within that State. All
actions and proceedings arising out of or relating to this Agreement shall be
heard and determined in a New York state or federal court sitting in the City
of New York, and the Parties hereby irrevocably submit to the exclusive
jurisdiction of such courts in any such action or proceeding and irrevocably
waive the defense of an inconvenient forum to the maintenance of any such
action or proceeding.

          SECTION 6.10. Counterparts. This Agreement may be executed (by
original or telecopied signature) in one or more counterparts, and by the
different Parties in separate counterparts, each of which when so executed
shall be deemed to be an original but all of which taken together shall
constitute one and the same agreement.

          SECTION 6.11. Specific Performance. The Parties agree that
irreparable damage would occur in the event any provision of this Agreement
was not performed in accordance with the terms hereof and that the parties
shall be entitled to specific performance of the terms hereof, in addition to
any other remedy at law or in equity.

          SECTION 6.12. Termination. This Agreement shall terminate on the
tenth anniversary of the date hereof. After the eighth anniversary hereof the
Parties shall use their commercially reasonable efforts to extend the terms of
this Agreement for an additional ten year period.

                                      25

<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed as of the date first written above by their respective officers
thereunto duly authorized.

                                             CLARK USA, INC.

                                             By:/s/ Katherine D. Knocke
                                                -----------------------------
                                                Name: Katherine D. Knocke
                                                Title: Secretary

                                             OCCIDENTAL C.O.B. PARTNERS

                                             By OXY USA, Inc.,
                                                  its managing partner

                                             By: /s/ David C. Yen
                                                -----------------------------
                                                Name: David C. Yen
                                                Title: Vice President and
                                                       Treasurer

          The undersigned hereby agrees to be bound by the provisions of
Article II hereof.

                                             BCP/CLARK HOLDINGS CORPORATION

                                             By: /s/ David Foley
                                                -----------------------------
                                                Name: David Foley
                                                Title: Secretary and Treasurer<PAGE>

                                                                   Exhibit 4.20

                             STOCKHOLDER AGREEMENT

     STOCKHOLDER AGREEMENT, dated as of March 9, 1999 (the "Agreement"), among
CLARK REFINING HOLDINGS INC., a Delaware corporation (the "Company" or "Clark"),
Blackstone Capital Partners III Merchant Banking Fund L.P., a Delaware limited
partnership (together with its affiliates, "Blackstone"); and Marshall A. Cohen,
an individual ("Holder").

     WHEREAS, Blackstone holds a majority of the outstanding shares of common
stock of the Company ("Shares"); and

     WHEREAS, on the date hereof, Holder is acquiring Shares as a result of
services rendered on behalf of the Company and other good and valuable
consideration;

     NOW, THEREFORE, in consideration of the mutual covenants and conditions as
hereinafter set forth, the parties hereto do hereby agree as follows:

I. REPRESENTATIONS AND WARRANTIES

     1.1 Representations and Warranties of the Company. The Company represents
and warrants to the Holder as follows:

     (a) the Company is a corporation duly incorporated, validly existing and in
good standing under the laws of the state of Delaware and has all requisite
corporate power and authority to execute and deliver this Agreement and to
perform its obligations hereunder. The execution and delivery by the Company of
this Agreement, the performance by the Company of its obligations hereunder, and
the consummation by the Company of the transactions contemplated hereby have
been duly authorized by all requisite corporate action. This Agreement has been
duly executed and delivered by the Company and, assuming the due authorization,
execution and delivery thereof by the Holder, constitutes a legal, valid and
binding obligation of the Company, enforceable against the Company in accordance
with its terms;

     (b) the execution, delivery and performance by the Company of this
Agreement and the consummation by the Company of the transactions contemplated
hereby do not and will not, with or without the giving of notice or the passage
of time or both, (i) violate the provisions of any law, rule or regulation
applicable to the Company or its assets, (ii) violate the provisions of the
certificate of incorporation or bylaws of the Company, as amended, or (iii)
violate any judgment, decree, order or award of any court, governmental or
quasi-governmental agency or arbitrator applicable to the Company or its assets;
and

     (c) no consent, approval, exemption or authorization is required to be
obtained from, no notice is required to be given to and no filing is required to
be obtained from any third party (including, without limitation, governmental
and quasi-governmental agencies, authorities and instrumentalities of competent
jurisdiction) by the Company, in order (i) for this Agreement to constitute a
legal, valid and binding obligation of the Company.

                                       1
<PAGE>

     1.2 Representations and Warranties of the Holder. The Holder represents and
warrants to the Company that:

     (a) this Agreement has been duly executed and delivered by the Holder and,
assuming the due authorization, execution and delivery thereof by the Company,
constitutes a legal, valid and binding obligation of the Holder, enforceable
against the Holder in accordance with its terms;

     (b) the execution, delivery and performance by the Holder of this Agreement
and the consummation by the Holder of the transactions contemplated hereby do
not and will not, with or without the giving of notice or the passage of time or
both, (i) violate the provisions of any law, rule or regulation applicable to
the Holder or its assets, or (ii) violate any judgment, decree, order or award
of any court, governmental or quasi-governmental agency or arbitrator applicable
to the Holder or its assets;

     (c) no consent, approval, or authorization is required to be obtained from,
no notice is required to be given to, and no filing is required to be obtained
from, any third party (including, without limitation, governmental and
quasi-governmental agencies, authorities and instrumentalities of competent
jurisdiction) by the Holder in order for this Agreement to constitute a legal,
valid and binding obligation of the Holder;

     (d) Holder is acquiring the Shares for investment solely for its own
account and not with a view to, or for resale in connection with, the
distribution or other disposition thereof;

     (e) the Holder is an "accredited investor" within the meaning of Rule 501
of Regulation D under the Securities Act of 1933, as amended, and the rules and
regulations promulgated thereunder, as the same may be amended from time to time
("Securities Act");

     (f) the Holder's financial situation is such that it can afford to bear the
economic risk of holding the Shares for an indefinite period of time, has
adequate means for providing for its current needs and contingencies, and can
afford to suffer a complete loss of its investment in the Shares;

     (g) the Holder's knowledge and experience in financial and business matters
are such that it is capable of evaluating the merits and risks of the investment
in the Shares;

     (h) the Holder understands that the Shares are a speculative investment
which involves a high degree of risk of loss of Holder's investment therein,
there are substantial restrictions on the transferability of the Shares, and, on
the date hereof and for an indefinite period following the date hereof, there
will be no public market for the Shares and, accordingly, it may not be possible
for the Holder to liquidate its investment in case of emergency, if at all;

     (i) the Holder understands and has taken cognizance of all the risk factors
related to the purchase of the Shares, and, other than as set forth in this
Agreement, no representations or warranties have been made to the Holder or its
representatives concerning the Shares or the Company or their prospects or other
matters;

     (j) the Holder has relied upon independent investigations made by it and,
to the extent believed by the Holder to be appropriate, its representatives,
including its own professional, financial, tax and other advisors;

     (k) the Holder has received information about the Company and been given
the opportunity to examine all documents and to ask questions of, and to receive
answers from, the Company and its representatives concerning the Company and the
terms and conditions of the purchase of the Shares and to obtain any additional
information which the Holder deems necessary; and

                                       2
<PAGE>

     (l) all information which the Holder has provided to the Company and its
representatives concerning the Holder and its financial position is complete and
correct as of the date of this Agreement.

II. TRANSFERS

     2.1 Limitations on Transfer. Holder hereby agrees that, except for any
transfer, sale, assignment, exchange, mortgage, pledge, hypothecation or other
disposition of any Common Stock or any interest therein ("Transfer") effected
pursuant to to an effective registration statement filed under the Securities
Act, no Transfer shall occur unless the Company has been furnished with an
opinion in form and substance reasonable satisfactory to the Company of counsel
reasonable satisfactory to the Company that such Transfer is exempt from the
provisions of Section 5 under the Securities Act.

     (b) Holder hereby agrees that, except for Transfers in connection with a
sale of shares of Common Stock to the public pursuant to an effective
registration statement filed under the Securities Act ("Public Offering"),
Transfers pursuant to Rule 144 (other than Rule 144(k)) under the Securities Act
and Transfers pursuant to Section 2.5 or 2.6, no Transfer shall occur unless the
transferee shall agree to become a party to, and be bound to the same extent as
its transferor by the terms of, Articles II and III of this Agreement.

     (c) Notwithstanding anything contained herein to the contrary, but subject
to Section 2.2, Holder hereby agrees that, in addition to the limitation on
transfer set forth in Section 2.8(a), no Transfer shall occur until eighteen
months after the date of Clark's initial underwritten Public Offering or such
earlier date after the such initial Public Offering on which an underwritten
registered secondary offering involving shares of Common Stock occurs.
Notwithstanding the foregoing, in the event Blackstone sells shares for its own
account in such initial Public Offering, Holder may transfer Shares in such
offering in accordance with Section 2.7 hereof, except that in such circumstance
clause (ii) of Section 2.7(b) shall be deemed to read as follows: (ii) second,
to the extent that the number of shares of Common Stock which are proposed to be
sold in such offering is less than the number of shares of Common Stock which
the Company has been advised can be sold in such offering without having the
adverse effect referred to above, the number of shares of Common Stock
Blackstone intends to dispose of in such offering shall have priority.

     2.2 Transfers to Affiliates. Notwithstanding anything contained herein to
the contrary, Holder shall be entitled from time to time to Transfer any or all
of the shares of Common Stock beneficially owned by Holder to Holder's spouse or
descendants, or to a trust in favor of Holder's spouse or descendants, or to any
other entity the owners of which consist exclusively of Holder, Holder's spouse,
Holder's descendants or such trusts ("Permitted Affiliate"), who, in each such
case, agree in a writing satisfactory in form and substance to the Company to
become a party to, and be bound to the same extent as its transferor by the
terms of, Articles II and III of this Agreement.

     2.3 Effect of Void Transfers. In the event of any purported Transfer of any
shares of Common Stock in violation of the provisions of this Agreement, such
purported Transfer shall be void and of no effect and the Company shall not give
effect to such Transfer.

     2.4 Legend on Securities. Each certificate representing shares of Common
Stock issued to Holder shall bear the following legend on the face thereof;

          "THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A
     SUBSCRIPTION AGREEMENT BETWEEN CLARK REFINING HOLDINGS INC. (THE
     "COMPANY"), AND ________________, A COPY OF WHICH IS ON FILE WITH THE
     SECRETARY OF THE COMPANY. NO TRANSFER, SALE, ASSIGNMENT, PLEDGE,
     HYPOTHECATION OR OTHER DISPOSITION OF THE SECURITIES REPRESENTED BY THIS
     CERTIFICATE

                                       3
<PAGE>

     MAY BE MADE EXCEPT IN ACCORDANCE WITH THE PROVISIONS OF SUCH SUBSCRIPTION
     AGREEMENT AND (A) PURSUANT TO A REGISTRATION STATEMENT EFFECTIVE UNDER THE
     SECURITIES ACT OF 1933, AS AMENDED, OR (B) IF THE COMPANY HAS BEEN
     FURNISHED WITH AN OPINION IN FORM AND SUBSTANCE REASONABLY SATISFACTORY TO
     THE COMPANY OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH
     TRANSFER, SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER DISPOSITION IS
     EXEMPT FROM THE PROVISIONS OF SECTION 5 OF THE SECURITIES ACT OF 1933, AS
     AMENDED, AND THE RULES AND REGULATIONS THEREUNDER. THE HOLDER OF THIS
     CERTIFICATE, BY ACCEPTANCE OF THIS CERTIFICATE, AGREES TO BE BOUND BY ALL
     OF THE PROVISIONS OF SUCH SUBSCRIPTION AGREEMENT."

     2.5 Tag-Along Rights. So long as this Agreement shall remain in effect and
Blackstone beneficially owns on a fully diluted basis an aggregate number of
shares of Common Stock not less than one-fourth (1/4) of the Common Stock owned
by Blackstone on the date hereof, with respect to any proposed Transfer by
Blackstone (in such capacity, a "Transferring Stockholder") of 25% or more of
the shares of Common Stock held by Blackstone, other than a Transfer to any
affiliate of Blackstone or any stockholder, partner or other equity owner of any
such affiliate or Blackstone or (ii) pursuant to a Public Offering, the
Transferring Stockholder shall have the obligation, and Holder and the Permitted
Affiliates shall have the right, to require the proposed transferee to purchase
from Holder and the Permitted Affiliates (in such capacity, a "Tagging
Stockholder") a number of the Shares up to the product (rounded up to the
nearest whole number) of (i) the quotient determined by dividing (A) the
aggregate number of Shares owned by Blackstone to be included in the
contemplated Transfer by (B) the aggregate number of shares owned by Blackstone
immediately prior to the contemplated Transfer, and the total number of shares
owned by the Tagging Stockholder, and at the same price per share of Common
Stock and upon the same terms and conditions (including without limitation time
of payment and form of consideration) applicable to the Transferring
Stockholder; provided, that in order to be entitled to exercise its right to
sell shares of Common Stock to the proposed transferee pursuant to this Section
2.5,the Tagging Stockholder must agree to make to the transferee the same
representations, warranties, covenants, indemnities and agreements that the
Transferring Stockholder agrees to make in connection with the proposed Transfer
of the shares of Common Stock of the Transferring Stockholder; and provided
further, that all representations and warranties shall be made by the Tagging
Stockholder and the Transferring Stockholder severally and not jointly and that
the liability of the Transferring Stockholder and the Tagging Stockholder
(whether pursuant to a representation, warranty, covenant, indemnification
provision or agreement) for liabilities in respect of the Company shall be
evidenced in writings executed by them and the transferee and shall be borne by
each of them on a pro rata basis.

                                       4
<PAGE>

     (b) The Transferring Stockholder shall give notice to Holder of each
proposed Transfer giving rise to the rights of the Tagging Stockholder set forth
in the first sentence of Section 2.5(a) at least 15 business days prior to the
proposed consummation of such Transfer, setting forth the number of shares of
Common Stock proposed to be so transferred, the name and address of the proposed
transferee, the proposed amount and form of consideration and the other terms
and conditions offered by the proposed transferee, and a representation that the
proposed transferee has been informed of the tag-along rights provided for in
this Section 2.5 and has agreed to purchase shares of Common Stock in accordance
with the terms hereof. The tag-along rights provided by this Section 2.5 must be
exercised by the Tagging Stockholder within 5 business days following receipt of
the notice required by the preceding sentence, by delivery of a written notice
to the Transferring Stockholder indicating such Tagging Stockholder's desire to
exercise its rights and specifying the number of shares of Common Stock it
desires to sell.

     (c) If the Tagging Stockholder exercises its rights under Section 2.5(a),
the closing of the purchase of the Registrable Securities with respect to which
such rights have been exercised shall take place concurrently with the closing
of the sale of the Transferring Stockholder's Common Stock.

     2.6 Drag-Along Rights. So long as this Agreement shall remain in effect and
Blackstone beneficially owns on a fully diluted basis an aggregate number of
shares of Common Stock not less than one-fourth (1/4) of the Common Stock owned
by Blackstone on the date hereof, if Blackstone receives an offer from a person
other than Holder or any of its affiliates (a "Third Party") to purchase 25% or
more of the shares of Common Stock owned by Blackstone and such offer is
accepted by Blackstone, then Holder hereby agrees that it will Transfer the
Applicable Number (as defined below) of Shares owned by it to such Third Party
upon the terms and conditions of the offer (including without limitation time of
payment and form of consideration) applicable to Blackstone, provided that
Holder must agree to make to the Third Party the same representations,
warranties, covenants, indemnities and agreements that Blackstone agrees to make
in connection with the proposed Transfer; and provided further, that all
representations and warranties shall be made by Holder and Blackstone severally
and not jointly and that the liability of Holder and Blackstone (whether
pursuant to a representation, warranty, covenant, indemnification provision or
agreement) for liabilities in respect of the Company shall be evidenced in
writings executed by them and the Third Party and shall be borne by each of them
on a pro rata basis. The "Applicable Number" shall mean a number (rounded up to
the nearest whole number) equal to the product of (i) quotient determined by
dividing (A) the aggregate number of shares owned by Blackstone to be included
in the contemplated Transfer by (B) the aggregate number of shares owned by
Blackstone immediately prior to the contemplated Transfer, and (ii) the total
number of shares owned by Holder.

     2.7 Piggyback Rights. Each time the Company is planning to file a
registration statement under the Securities Act in connection with the proposed
offer and sale of Common Stock by the Company and/or Blackstone (other than
under Form S-8 or Form S-4 or a similar successor form), the Company will give
prompt written notice thereof to Holder regarding Holder's rights under this
Section 2.7, at least 15 business days prior to the anticipated filing date of
such registration statement; provided, that Holder and its affiliates shall have
no rights pursuant to this Section 2.7 with respect to the first Public Offering
of Common Stock if the Company is the only Person including shares of Common
Stock in such registration statement. Upon the written request of Holder or the
Permitted Affiliates made within 5 business days after the receipt of any such
notice from the Company, which request shall specify the number of Shares (the
"Holder Piggy-Back Shares") intended to be disposed of by Holder or the
Permitted Affiliates in such offering, the Company will use its reasonable
efforts to effect the registration under the Securities Act of all Holder
Piggy-Back Shares which the Company has been so requested to register by Holder,
to the extent required to permit the disposition of the Holder Piggy-Back Shares
to be registered; provided, that if, at any time after giving written notice of
its intention to register any Common Stock and prior to the effective date of
the registration statement filed in connection with such registration, the
Company or Blackstone shall determine for any reason not to proceed with the
proposed

                                       5
<PAGE>

registration, the Company may at its election give written notice of such
determination to the holder of Holder Piggy-Back Shares and thereupon shall be
relieved of its obligation to register any Holder Piggy-Back Shares in
connection with such registration and if such registration involves an
underwritten offering, the holder of Holder Piggy-Back Shares requesting to be
included in the registration must sell its shares to the underwriters on the
same terms and conditions as apply to the Company and/or Blackstone.

     (b) If a registration pursuant to this Section 2.7 involves an underwritten
offering and the managing underwriter or underwriters in good faith advise the
Company in writing that, in their opinion, the number of shares of Common Stock
which the Company, Blackstone and the holder of Holder Piggy-Back Shares intend
to include in such registration exceeds the number of shares of Common Stock
which can be sold in such offering without having an adverse effect on such
offering (including the price at which the shares of Common Stock can be sold),
then the Company will include in such registration first, 100% of the shares the
Company proposes to sell for its own account, if any, and 100% of the shares of
any person exercising demand registration rights (other than Blackstone), if
any, and second, to the extent that the number of shares described under clause
(i) is less than the number of shares of Common Stock which the Company has been
advised can be sold in such offering without having the adverse effect referred
to above, the number of shares Blackstone intends to dispose of in such
offering, the Holder Piggy-Back Shares and shares of any other person exercising
similar piggy-back registration rights, on a pro rata basis.

     2.8 Other Registration-Related Matters.

     (a) Holder agrees that it shall not effect any direct or indirect Transfer
of Common Stock during the 14 days prior to or the 180 day period beginning on
the effective date of a registration statement (whether pursuant to Section 2.7
or otherwise, except as part of such registration) if and to the extent
reasonably requested in writing by the managing underwriter of the underwritten
public offering.

     (b) The Company agrees not to effect any direct or indirect Transfer of
Common Stock during the 14 days prior to and the 180 day period beginning on the
effective date of any registration statement in which Holder is participating
pursuant to Section 2.7 in connection with an underwritten public offering of
Common Stock, if and to the extent reasonably requested in writing by the
managing underwriter of the underwritten public offering.

     (c) The Company may require any Person that is selling shares of Common
Stock in a Public Offering to furnish to the Company such information regarding
such Person and the distribution of the shares of Common Stock which are
included in a Public Offering as may from time to time reasonably be requested
in writing in order to comply with the Securities Act.

III. OTHER

     3.1 Additional Securities Subject to Agreement. Holder agrees that all
shares of Common Stock which it shall hereafter acquire by means of a stock
split, stock dividend, distribution or otherwise (other than pursuant to a
Public Offering) shall be subject to the provisions of this Agreement to the
same extent as if held on the date hereof.

     3.2 Termination. This Agreement shall terminate, and thereby become null
and void, in full on the earliest date on which Blackstone does not beneficially
own in the aggregate at least 5% of the Common Stock outstanding on a fully
diluted basis.

     3.3 Injunctive Relief. Holder acknowledges and agrees that a violation of
any of the terms of this Agreement will cause the Company and Blackstone
irreparable injury for which adequate remedy at law is not available.
Accordingly, it is agreed that the Company or Blackstone shall be entitled to an
injunction, restraining order or other equitable relief to prevent breaches of
the provisions of this Agreement and to enforce specifically the terms and
provisions hereof in any court of competent

                                       6

<PAGE>

jurisdiction in the United States or any state thereof, in addition to any other
remedy to which they may be entitled at law or equity.

     3.4 Other Stockholders' Agreements. Holder shall not enter into any
stockholder agreement or other arrangement of any kind with any person with
respect to shares of Common Stock, and Holder represents and warrants that it
has not previously entered into such an agreement that remains in full force and
effect as of the date hereof which is inconsistent with the provisions of this
Agreement or which may impair its ability to comply with this Agreement.

     3.5 Amendments. This Agreement may be amended only by a written instrument
signed by each party hereto.

     3.6 Successors, Assigns and Transferees. The provisions of this Agreement
shall be binding upon and shall inure to the benefit of the parties hereto and
their respective successors and transferees permitted hereunder (except for
transferees that are transferred Common Stock pursuant to a Public Offering,
pursuant to Rule 144 under the Securities Act or pursuant to Section 2.5 or
2.6), each of which shall agree in writing to become a party hereto and be bound
to the same extent hereby as the transferor that has transferred the Common
Stock to such transferees; provided, that if Holder transfers a portion of its
Common Stock to one or more transferees which are entitled to rights of the
transferor hereunder, then such transferee(s) shall exercise such rights as a
single group with that transferor and its affiliates; provided further, that the
rights granted to the Holder in Sections 2.5 and 2.7 can only be transferred to
Permitted Affiliates.

     3.7 Notices. All notices, requests and demands to or upon the respective
parties hereto to be effective shall be in writing (including by telecopy), and,
unless otherwise expressly provided herein, shall be deemed to have been duly
given or made when delivered by hand, or two days after being delivered to a
recognized courier (whose stated terms of delivery are three days or less to the
destination of such notice) or, in the case of telecopy notice, when received,
addressed as follows to the parties hereto, or to such other address as may be
hereafter notified by the respective parties hereto:

        When Holder is the intended recipient:

                Mr. Marshall A. Cohen
                Cassel Brock & Blackwell
                Scotia Plaza, Suite 2200
                40 King Street West
                Toronto, Ontario M5H-3C2 Canada
                Telecopy: 416-860-2900

                                       7

<PAGE>

        When the Company is the intended recipient:

                Clark Refining Holdings Inc.
                8182 Maryland Avenue
                St. Louis, Missouri 63105
                Attention: Maura J. Clark
                Telecopy: (314) 854-1570

        with a copy to:

                Simpson Thacher & Bartlett
                425 Lexington Avenue
                New York, New York 10017
                Attention: Wilson S. Neely
                Telecopy: (212) 455-2502

     3.8 Integration. This Agreement, and the documents referred to herein or
delivered pursuant hereto, contain the entire understanding of the parties with
respect to the subject matter hereof. If there is any conflict between the
Company's stock option or incentive plans and this Agreement, the provisions of
this Agreement shall control. There are no agreements, representations,
warranties, covenants or undertakings with respect to the subject matter hereof
other than those expressly set forth herein. This Agreement supersedes all other
prior agreements and understandings between the parties with respect to such
subject matter.

     3.9 Severability. If one or more of the provisions, paragraphs, words,
clauses, phrases or sentences contained herein, or the application thereof in
any circumstances, is held invalid, illegal or unenforceable in any respect for
any reason, the validity, legality and enforceability of any such provision,
paragraph, word, clause, phrase or sentence in every other respect and of the
remaining provisions, paragraphs, words, clauses, phrases or sentences hereof
shall not be in any way impaired, it being intended that all rights, powers and
privileges of the parties hereto shall be enforceable to the fullest extent
permitted by law.

     3.10 Counterparts. This Agreement may be executed in two or more
counterparts, and by different parties on separate counterparts, each of which
shall be deemed an original, but all of which shall constitute one and the same
instrument.

     3.11 Governing Law. This Agreement shall be governed by and construed and
enforced in accordance with the laws of the State of New York without regard to
the conflicts of law principles thereof. The parties executing this Agreement
hereby agree to submit to the non-exclusive jurisdiction of the federal and
state courts located in the State of New York in any action or proceeding
arising out of or relating to this Agreement.

     3.12 Voting. Holder hereby agrees that, so long as this Agreement shall
remain in effect, it will vote all of the Common Stock beneficially owned or
held of record by it to ratify, approve and adopt any and all actions (including
without limitation the election of directors) adopted or approved by Blackstone.

                                       8

<PAGE>

        IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the day and year first above written.

                          CLARK REFINING HOLDINGS INC.

                          By: /s/ William C. Rusnack
                             -------------------------------------------------
                             Name:  William C. Rusnack
                             Title: Chief Executive Officer

                          BLACKSTONE CAPITAL PARTNERS III
                            MERCHANT BANKING FUND L.P.

                            By: Blackstone Management Associates III, L.L.C.,
                                its general partner

                            By: /s/ Robert L. Friedman
                               ----------------------------------------------
                               Name:  Robert L. Friedman
                               Title: Member

                          /s/ Marshall A. Cohen
                          ---------------------------------------------------
                          Marshall A. Cohen

                                       9

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