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                                                                   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.


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     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


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     (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


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     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.


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     (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


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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


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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



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        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.


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        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





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