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                                                                    EXHIBIT 4.18

                      AMENDMENT OF INTERCREDITOR AGREEMENT

         THIS AMENDMENT OF INTERCREDITOR AGREEMENT (this "Amendment"), dated as
of July 22, 1999, among CHASE BANK OF TEXAS, N.A. (formerly known as Texas
Commerce Bank National Association), as Administrative Agent (the
"Administrative Agent"), STERLING CHEMICALS HOLDINGS, INC., a Delaware
corporation (the "Company"), and STATE STREET BANK AND TRUST COMPANY, as
Trustee (in such capacity, the "Trustee").

                             PRELIMINARY STATEMENTS

     A.  The Company and Fleet National Bank, as Trustee, (the "Initial
         Trustee"), entered into that certain Indenture dated as of August 15,
         1996 (as heretofore amended, the "Indenture") providing, among other
         things, for the issuance of the Company's 13 1/2% Senior Secured
         Discount Notes Due 2008 in the aggregate principal amount of
         $191,751,000 (the "Discount Notes"). Capitalized terms used but not
         defined herein shall have the meanings specified for such terms in the
         Indenture.

     B.  The Trustee has prior to the date hereof replaced the Initial Trustee
         as the Trustee under the Indenture.

     C.  On June 21, 1996, STX Chemicals Corp., a Delaware corporation and a
         wholly-owned subsidiary of the Company that is now known as Sterling
         Chemicals, Inc. ("Chemicals"), and certain of its Affiliates entered
         into that certain Credit Agreement (as heretofore amended, the "Credit
         Agreement") dated as of June 21, 1996 with the Administrative Agent,
         and the Lenders named therein, pursuant to which, among other things,
         the Lenders named therein committed to lend Chemicals an aggregate
         amount of up to $456,500,000. In connection with the Credit Agreement
         and the Indenture, the Administrative Agent and the Initial Trustee
         entered into that certain Intercreditor Agreement dated as of August
         21, 1996 (the "Intercreditor Agreement").

     D.  The Company and its Restricted Subsidiaries plan to refinance the
         indebtedness outstanding under the Credit Agreement by, among other
         things, incurring indebtedness under a new Revolving Credit Agreement,
         dated as of July 23, 1999 (as amended, supplemented, amended and
         restated or otherwise modified from time to time, the "New Credit
         Agreement"), to be entered into among Chemicals, certain other Wholly
         Owned Subsidiaries of the Company, the various financial institutions
         from time to time parties thereto (the "New Lenders"), the CIT
         Group/Business Credit, Inc., as the Administrative Agent (the "New
         Administrative Agent"), Credit Suisse First Boston, as the
         Documentation Agent, and DLJ Capital Funding, Inc., as the Syndication
         Agent, pursuant to which Chemicals or any such Wholly Owned Subsidiary
         could borrow, on a revolving credit basis, up to $155,000,000 under
         (A) an
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         $85,000,000 revolving credit facility secured by the accounts
         receivable and inventory of Chemicals and such Wholly Owned
         Subsidiaries (the "Working Capital Revolver") and (B) a $70,000,000
         revolving credit facility which would be secured by a first priority
         pledge on the fixed assets and capital stock of Chemicals and such
         Wholly Owned Subsidiaries (the "Fixed Assets Revolver") and the
         Amendment is a condition precedent to the making of loans under, and
         the effectiveness of, the New Credit Agreement.

     E.  Pursuant to Section 10.01 of the Indenture, the Company and the Trustee
         may amend or supplement the Intercreditor Agreement, without the
         consent of any Holder of a Discount Note, to, among other things, cure
         any ambiguity, omission, defect or inconsistency.

     F.  The Company has determined that the Intercreditor Agreement contains
         certain ambiguities, omissions, defects and/or inconsistencies with
         respect to the ability of the Company to secure any refinancing of the
         Lender Liabilities (as defined in the Intercreditor Agreement) with a
         pledge of Collateral (as defined in the Intercreditor Agreement) having
         the same priority as the priority of the security interest in the
         Collateral held by the Lenders under the Credit Agreement.

     G.  Pursuant to Section 10.01 of the Indenture, upon the request of the
         Company accompanied by a resolution of the Board of Directors
         authorizing the execution of an amendment of the Intercreditor
         Agreement, and upon receipt of certain documents by the Trustee, the
         Trustee is required to join in the execution of any amendment of the
         Intercreditor Agreement authorized or permitted by the terms of the
         Indenture.

     H.  The Board of Directors of the Company has authorized the execution of
         this Amendment and, simultaneously with and as a condition to the
         execution of this Amendment by the Trustee, the Company is delivering
         to the Trustee resolutions of the Board of Directors authorizing the
         execution of this Amendment and an Officer's Certificate and Opinion of
         Counsel, each in the form required by the Indenture and satisfactory to
         the Trustee.

     I.  All acts and things necessary to make the Intercreditor Agreement, as
         amended hereby, a valid, binding and legal agreement according to its
         terms have been done and performed.

         NOW THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Company covenants and agrees with the Administrative Agent and
the Trustee, for the equal and proportionate benefit of the respective Holders
from time to time of the Discount Notes, as follows:

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                                    ARTICLE I

                      Amendment of Intercreditor Agreement

         Section 1.01. Amendments of Intercreditor Agreement. The Intercreditor
Agreement is hereby amended so that:

         (a) each term contained in the Intercreditor Agreement (or incorporated
     therein by reference) which describes, defines or pertains or relates to
     any form of indebtedness or liability under the Credit Agreement or any
     other Loan Document (as defined in the Intercreditor Agreement) (including,
     but not limited to, the definitions of "Lender Liabilities" and
     "Commitments") shall, for all purposes of the Intercreditor Agreement, also
     include any indebtedness or liabilities of the Company and its Restricted
     Subsidiaries at any time and from time to time issued or incurred (i) to
     refinance, extend, renew, rearrange, refund, repay, redeem, defease, retire
     or replace the indebtedness or liabilities under the Credit Agreement or
     any other Loan Document (including any indebtedness or liabilities under
     the Fixed Assets Revolver) or (ii) in connection with any subsequent
     refinancing, extension, renewal, rearrangement, refunding, repayment,
     redemption, defeasance, retirement or replacement of any such indebtedness
     or liabilities referred to in clause (i) or this clause(ii) (the
     indebtedness and liabilities referred to clauses (i) and (ii) above,
     collectively, "Refinancing Debt"); provided that, in no event shall the
     aggregate indebtedness under any Refinancing Debt at any time outstanding
     exceed $456,500,000;

         (b) each term contained in the Intercreditor Agreement (or incorporated
     therein by reference) which describes, defines or pertains or relates to
     any document governing, evidencing or otherwise related to any indebtedness
     or liabilities under the Credit Agreement or any other Loan Document
     (including, but not limited to, the definitions of "Credit Agreement,"
     "Loan Documents," Financing Documents" and "Lender Notes") shall, for all
     purposes of the Intercreditor Agreement, also include any document from
     time to time governing, evidencing or otherwise related to any Refinancing
     Debt (including the New Credit Agreement and the Parent Pledge Agreement,
     dated as of July 23, 1999 (the "Parent Pledge Agreement"), between the New
     Administrative Agent and the Company, as amended, supplemented, amended and
     restated or otherwise modified from time to time, to the extent that the
     same governs the Fixed Assets Revolver and the notes evidencing the
     indebtedness under the Fixed Assets Revolver); or

         (c) each term contained in the Intercreditor Agreement (or incorporated
     therein by reference) which describes, defines or pertains or relates to
     any person or entity from time to time serving in any capacity or holding
     any indebtedness or liabilities under the Credit Agreement or any Loan
     Document or holding any Collateral (as defined in the Intercreditor
     Agreement) (including, but not limited to, the definitions of
     "Administrative Agent," "Issuing Banks" and "Lenders") shall, for all
     purposes of the Intercreditor Agreement, also include any person or entity
     from time to time serving in any capacity or holding any indebtedness or
     liabilities under any document governing, evidencing or otherwise related

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     to any Refinancing Debt (including the agents, issuers and lenders under
     the New Credit Agreement).

         Section 1.02. Effect of Amendments. Upon the effectiveness of this
Amendment, (a) any and all indebtedness and liabilities under or pertaining to
Refinancing Debt and any Collateral securing the same shall be entitled to the
benefits, priorities and protection provided, or purported to be provided, by
the Intercreditor Agreement to the same extent as if such indebtedness and
liabilities were the original "Lender Liabilities" thereunder and the Collateral
was Collateral for such original "Lender Liabilities", (b) any document
governing, evidencing or otherwise related to any Refinancing Debt (including
the New Credit Agreement to the extent that the same governs the Fixed Assets
Revolver, the notes evidencing the indebtedness under the Fixed Assets Revolver
and any security or pledge agreement granting or continuing any security
interest in the Collateral to secure such indebtedness and any related
liabilities) shall be entitled to the benefits, priorities and protection
provided, or purported to be provided, by the Intercreditor Agreement to the
same extent as if such documents were the original "Credit Agreement," "Loan
Documents," "Financing Documents," "Lender Notes" and "Collateral" thereunder
and (c) any person or entity serving in any capacity, holding any indebtedness
under any document governing, evidencing or otherwise related to such
Refinancing Debt or holding, directly or indirectly, any Collateral to secure
such indebtedness (including the agents, issuers and lenders under the New
Credit Agreement and the Parent Pledge Agreement) shall be entitled to the
benefits, priorities and protection provided, or purported to be provided, by
the Intercreditor Agreement to the same extent as if such persons and entities
were the original "Administrative Agent," "Issuing Banks" and "Lenders"
thereunder.

         Section 1.03. Effectiveness. This Amendment shall not be or become
effective unless and until the parties hereto have executed and delivered this
Agreement in the space provided below. Concurrently with the effectiveness of
the New Credit Agreement, the Administrative Agent shall be directed to transfer
the Collateral to the New Administrative Agent who shall hold such Collateral
pursuant to the terms of the Intercreditor Agreement as amended.

                                   ARTICLE II

                                   The Trustee

         The Trustee hereby accepts the trusts declared and provided in this
Amendment, upon the terms and conditions contained in the Indenture and Security
Documents (including the Intercreditor Agreement) as supplemented. All of the
provisions of the Indenture and the Intercreditor Agreement with respect to the
rights, privileges, immunities, powers and duties of the Trustee shall be
applicable in respect of this Amendment as fully and with the same effect as if
set forth herein in full. The Trustee shall not be responsible for and makes no
representation as to the validity or adequacy of this Amendment, the
authorization, or permissibility of this Amendment pursuant to the terms of the
Indenture or the Intercreditor Agreement, the due execution hereof by the
Company or for or in respect of the recitals or statements contained

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herein (other than the statements being made solely by the Company. The Trustee
shall not be responsible in any manner to determine the correctness or
provisions contained in this Amendment.

                                   ARTICLE III

                   Effect of Execution and Delivery Hereof

         From time after and execution and delivery of this Amendment, (i) the
Intercreditor Agreement shall be deemed to be modified as provided herein, (ii)
this Amendment shall form a part of the Indenture and Security Documents
(including the Intercreditor Agreement), (iii) except as modified by this
Amendment, the Indenture and Security Documents (including the Intercreditor
Agreement) shall continue in full force and effect, and (iv) every Holder of
Discount Notes heretofore and hereafter authenticated and delivered under the
Indenture shall be bound by this Amendment.

                                   ARTICLE IV

                            Miscellaneous Provisions

         Section 4.01 Headings. The headings of the Articles and Sections of
this Amendment have been inserted for convenience only, and shall not, for any
reason, be deemed to be part of this Amendment and shall in no way modify or
restrict any of the terms or provisions hereof.

         Section 4.02 Counterparts. This Amendment may be executed in any number
of counterparts and by the different parties hereto on separate counterparts,
each of which when so executed and delivered in original form or by facsimile or
other electronic means shall be an original, but all of which shall together
constitute one and the same instrument.

         Section 4.03 Successors and Assigns. All agreements of the Company
contained in this Amendment shall bind the Company and its successors. All
agreements of the Trustee in this Amendment shall bind the Trustee and its
successors. This Amendment shall be binding upon and inure to the benefit of and
be enforceable by the Holders of any Discount Notes then Outstanding.

         Section 4.04 Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT GIVING
EFFECT TO APPLICABLE PRINCIPLES OF CONFLICT OF LAW TO THE EXTENT THAT THE
APPLICATION OF THE LAW OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed, and their respective corporate seals to be hereunto affixed and
attested, all as of the day and first year above written.

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                                CHASE BANK OF TEXAS, N.A., as Administrative
                                  Agent

                                [SEAL]

                                By:
                                Title


                                ATTEST:


                                By:
                                Title:


                                STERLING CHEMICALS HOLDINGS, INC.

                                [SEAL]

                                By:
                                Title:


                                ATTEST:


                                By:
                                Title:


                                STATE STREET BANK AND TRUST COMPANY
                                   As Trustee

                                [SEAL]

                                By:
                                Printed Name:
                                Title:


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