<PAGE>

                                                                    Exhibit 10.7

                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                  This AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT (this
"ASSIGNMENT AND ACCEPTANCE") dated as of September 22, 2003 is made between Bank
of America, N.A. (the "ASSIGNOR"), each party identified on each signature page
hereto an assignee (each an "ASSIGNEE" and collectively the "ASSIGNEES"), and
the Borrowers and the Guarantors, each as hereinafter defined.

                                    RECITALS

                  WHEREAS, the Assignor is party to that certain Credit
Agreement dated as of July 31, 2003 (as amended, amended and restated, modified,
supplemented, or renewed, the "CREDIT AGREEMENT") by and among Westlake Chemical
Corporation and certain of its domestic subsidiaries listed as Borrowers thereto
(collectively, the "BORROWERS"), the several financial institutions from time to
time party thereto (including the Assignor, the "LENDERS"), and Bank of America,
N.A., as agent for the Lenders (the "AGENT"). Any terms defined in the Credit
Agreement and not defined in this Assignment and Acceptance are used herein as
defined in the Credit Agreement;

                  WHEREAS, as provided under the Credit Agreement, the Assignor
has committed to make Revolving Loans (the "REVOLVING COMMITTED LOANS") to the
Borrowers in an aggregate amount not to exceed $200,000,000 (the "REVOLVING
COMMITMENT");

                  WHEREAS, the Assignor has acquired a participation in its pro
rata share of the Letter of Credit Issuer's liabilities under Letters of Credit
in an aggregate principal amount of $14,500,322.50 (the "L/C OBLIGATIONS");

                  WHEREAS, the Assignor wishes to assign to each Assignee part
of the rights and obligations of the Assignor under the Credit Agreement in
respect of its Revolving Commitment, together with a corresponding portion of
each of its outstanding Revolving Committed Loans and L/C Obligations, in the
amounts set forth on each Assignee's signature page hereto (the "ASSIGNED
AMOUNT") on the terms and subject to the conditions set forth herein and each
Assignee wishes to accept assignment of such rights and to assume such
obligations from the Assignor on such terms and subject to such conditions; and

                  WHEREAS, in connection with the assignments made herein,
Lenders, Agent, Borrowers, and Guarantors wish to make certain modifications to
the Credit Agreement, as set forth herein.

                  NOW, THEREFORE, in consideration of the foregoing and the
mutual agreements contained herein, the parties hereto agree as follows:

         1.       Amendments.

                  (a)      The cover page of the Credit Agreement shall be
amended by adding "Credit Suisse First Boston, as Documentation Agent" thereto
immediately following "Bank of America, N.A., as the Agent".

                  (b)      SECTION 1.4 of the Credit Agreement shall be amended
in its entirety to read as follows:

                  1.4      Bank Products. The Borrowers may request and the
         Agent or Lenders may, in their sole and absolute discretion, arrange
         for the Borrowers to obtain from the Bank or the

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

         Bank's Affiliates or the Lenders or the Lenders' Affiliates, Bank
         Products, although the Borrowers are not required to do so. If Bank
         Products are provided by an Affiliate of the Bank or any Lender, the
         Borrowers agree to indemnity and hold the Agent, the Bank, and the
         Lenders harmless from any and all costs and obligations now or
         hereafter incurred by the Agent, the Bank, or any of the Lenders which
         arise from any indemnity given by the Agent to its Affiliates related
         to such Bank Products; provided, however, nothing contained herein is
         intended to limit any Borrower's rights, with respect to the Bank, any
         Lender or their respective Affiliates, as the case may be, which relate
         to Bank Products or the provision of the Bank Products pursuant
         thereto. The agreement contained in this Section shall survive
         termination of this Agreement. Each Borrower acknowledges and agrees
         that the obtaining of Bank Products from the Bank, any Lender or their
         respective Affiliates (a) is in the sole and absolute discretion of the
         Bank, any Lender, or their respective Affiliates, and (b) is subject to
         all rules and regulations of the Bank, any Lender, or their respective
         Affiliates.

                  (c)      SECTION 6.7 of the Credit Agreement shall be amended
in its entirety to read as follows:

                  6.7      Capitalization. Westlake's authorized capital stock
         consists of 10,000 shares of common stock, par value $1.00 per share of
         which 1,115 shares are validly issued and outstanding, fully paid and
         non-assessable and are owned beneficially and of record by Parent and
         1,000 shares of preferred stock, no par value, of which 890 shares are
         validly issued and outstanding, fully paid and non-assessable, and 770
         are owned beneficially and of record by Parent and 120 are owned of
         record by Wilmington Trust Company, as Trustee of the Chamly Birch
         Trust.

                  (d)      SECTION 7.21 of the Credit Agreement shall be amended
in its entirety to read as follows:

                           7.21     Fixed Charge Coverage Ratio. Effective on
         and after the Triggering Date and based on the most recently delivered
         Financial Statements received pursuant to SECTION 5.2, the Borrowers
         will maintain a Fixed Charge Coverage Ratio for each period of
         immediately preceding twelve (12) months of not less than 1.00 to 1.0.

                  (e)      The proviso set forth in the paragraph immediately
following SECTION 11.1(A)(IX) of the Credit Agreement shall be amended in its
entirety to read as follows:

         provided, however, the Agent may, in its sole discretion and
         notwithstanding the limitations contained in CLAUSES (V) and (IX) above
         (other than the limitations restricting the increase in the Maximum
         Revolver Amount) and any other terms of this Agreement, make Agent
         Advances in accordance with SECTION 1.2(i) and, provided further, that
         (A) no amendment, waiver, or consent shall, unless in writing and
         signed by the Agent, affect the rights or duties of the Agent under
         this Agreement or any other Loan Document; (B) no amendment shall
         increase the Commitment of any Lender unless consented to by such
         Lender; and (C) SCHEDULE 1.2 hereto (Commitments) may be amended from
         time to time by Agent alone to reflect assignments of Commitments in
         accordance herewith.

                  (f)      Section 12.20 of the Credit Agreement shall be
amended in its entirety to read as follows:

                           12.20    Co-Agents. None of the Lenders identified on
the facing page or signature pages of this Agreement as a "co-agent" or
"documentation agent" (if any) shall have any right, power, obligation,
liability, responsibility or duty under this Agreement other than those
applicable to all

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       2

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Lenders as such. Without limiting the foregoing, none of the
Lenders so identified as a "co-agent" or "documentation agent" (if any) shall
have or be deemed to have any fiduciary relationship with any Lender. Each
Lender acknowledges that it has not relied, and will not rely, on any of the
Lenders so identified in deciding to enter into this Agreement or in taking or
not taking action hereunder.

                  (g)      The last three sentences of SECTION 13.7 of the
Credit Agreement shall be amended in their entirety to read as follows:

         In addition, the Borrowers agree to pay costs and expenses incurred by
         the Agent, the Arranger, and the Lenders (including Attorneys' Costs)
         to the Agent, the Arranger, and the Lenders as applicable, for their
         respective benefit, on demand, and all reasonable fees, expenses and
         disbursements incurred by Agent, the Arranger, and the Lenders for any
         law firm retained by the Agent, the Arranger, or any Lender, in each
         case, paid or incurred to obtain payment of the Obligations, enforce
         the Agent's Liens, sell or otherwise realize upon the Collateral, and
         otherwise enforce the provisions of the Loan Documents, or to defend
         any claims made or threatened against the Agent, the Arranger, or any
         Lender arising out of the transactions contemplated hereby (including
         preparations for and consultations concerning any such matters). The
         foregoing shall not be construed to limit any other provisions of the
         Loan Documents regarding costs and expenses to be paid by the Borrower.
         All of the foregoing costs and expenses may be (in the sole discretion
         of the Agent) charged to the Borrowers' Loan Account as Revolving Loans
         as described in SECTION 3.7 up to the Maximum Revolver Amount.

                  (h)      The definition of "Bank Products" set forth in ANNEX
A to the Credit Agreement shall be amended in its entirety to read as follows:

                  "BANK PRODUCTS" means any one or more of the following types
of services or facilities extended to any Loan Party by a Lender or any
Affiliate of a Lender in reliance on the Lender's agreement to indemnify such
Affiliate: (i) credit cards; (ii) ACH Transactions; (iii) cash management,
including controlled disbursement services; and (iv) Hedge Agreements.

                  (i)      The definition of "Bank Product Reserves" set forth
in ANNEX A to the Credit Agreement shall be amended in its entirety to read as
follows:

                  "BANK PRODUCT RESERVES" means all Reserves which the Agent
from time to time establishes in its reasonable discretion for the Bank Products
then provided or outstanding; provided that, without limiting the foregoing, (a)
the Agent shall not be required to establish any Bank Product Reserve with
respect to any Bank Products provided by any Lender (or any of its Affiliates)
for which the applicable Lender has not requested that the Agent establish a
Reserve with respect thereto in advance of actually providing such Bank Products
to any Loan Party, (b) the amount of any Bank Product Reserve requested by any
Lender shall be reasonable in light of the circumstances, and (c) the Agent
shall not be responsible for adjusting the amount of any Bank Product Reserve
from time to time without notice from the applicable Lender to make any such
adjustment.

                  (j)      The definition of "Excess Cash Flow Prepayment" set
forth in ANNEX A to the Credit Agreement shall be amended in its entirety to
read as follows:

                  "EXCESS CASH FLOW PREPAYMENT" means any prepayment of the
         Fixed Asset Loan from "Excess Cash Flow," as defined in and as set
         forth in Section 2.04(b)(i) of the Fixed Asset Loan credit agreement on
         the Closing Date.

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       3

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                  (k)      The definition of "Fixed Asset Loan" set forth in
ANNEX A to the Credit Agreement shall be amended by inserting "31" in the date
to read "July 31, 2003".

                  (l)      The definition of Pro Rata Share set forth in ANNEX A
to the Credit Agreement shall be amended in its entirety to read as follows:

                           "PRO RATA SHARE" means, with respect to a Lender, a
         fraction (expressed as a percentage), the numerator of which is the
         amount of such Lender's Commitment and the denominator of which is the
         sum of the amounts of all of the Lenders' Commitments, or if no
         Commitments are outstanding, a fraction (expressed as a percentage),
         the numerator of which is the amount of Obligations owed to such Lender
         (excluding any Obligations with respect to Bank Products) and the
         denominator of which is the aggregate amount of the Obligations owed to
         the Lenders (excluding any Obligations with respect to Bank Products),
         in each case giving effect to a Lender's participation in Non-Ratable
         Loans and Agent Advances.

                  (m)      The references to "Texas" set forth in SECTION 10(e)
of EXHIBIT F to the Credit Agreement shall be amended to read "New York".

                  (n)      SCHEDULE 1.2 of the Credit Agreement shall be amended
in its entirety and replaced with SCHEDULE 1.2 attached hereto.

         2.       Assignment and Acceptance.

                  (a)      Subject to the terms and conditions of this
Assignment and Acceptance, (i) the Assignor hereby sells, transfers, and assigns
to each Assignee, and (ii) each Assignee hereby purchases, assumes, and
undertakes from the Assignor, without recourse and without representation or
warranty (except as provided in this Assignment and Acceptance) the percentage
set forth on each Assignee's signature page hereto (the "ASSIGNEE'S PERCENTAGE
SHARE") of (A) the Revolving Commitment, the Revolving Committed Loans, and the
L/C Obligations of the Assignor and (B) all related rights, benefits,
obligations, liabilities, and indemnities of the Assignor under and in
connection with the Credit Agreement and the Loan Documents.

                  (b)      With effect on and after the Effective Date (as
defined in SECTION 5 hereof), each Assignee shall be a party to the Credit
Agreement and succeed to all of the rights and be obligated to perform all of
the obligations of a Lender under the Credit Agreement, including the
requirements concerning confidentiality and the payment of indemnification, with
a Revolving Commitment in an amount equal to the Assigned Amount. Each Assignee
agrees that it will perform in accordance with their terms all of the
obligations which by the terms of the Credit Agreement are required to be
performed by it as a Lender. It is the intent of the parties hereto that the
Revolving Commitment of the Assignor shall, as of the Effective Date, be reduced
by an amount equal to the Assigned Amount, and the Assignor shall relinquish its
rights and be released from its obligations under the Credit Agreement to the
extent such obligations have been assumed by the Assignees; provided, however,
the Assignor shall not relinquish its rights under SECTIONS 3.8, 4, and 13.11 of
the Credit Agreement to the extent such rights relate to the time prior to the
Effective Date.

                  (c)      After giving effect to the assignment and assumption
set forth herein, on the Effective Date each Assignee's Revolving Commitment and
Revolving Committed Loans will be in the amounts set forth on their signature
page attached hereto.

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       4

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         3.       Reallocation of Payments.

                  Any interest, fees, and other payments accrued to the
Effective Date with respect to the Revolving Commitment, Revolving Committed
Loans, and L/C Obligations shall be for the account of the Assignor. Any
interest, fees, and other payments accrued on and after the Effective Date with
respect to the Assigned Amount shall be for the account of each Assignee. Each
of the Assignor and Assignees agrees that it will hold in trust for the other
party any interest, fees, and other amounts which it may receive to which the
other party is entitled pursuant to the preceding sentence and pay to the other
party any such amounts which it may receive promptly upon receipt.

         4.       Independent Credit Decision.

                  Each Assignee (a) acknowledges that it has received a copy of
the Credit Agreement and the Schedules and Exhibits thereto, together with
copies of the most recent Financial Statements of the Loan Parties, and such
other documents and information as it has deemed appropriate to make its own
credit and legal analysis and decision to enter into this Assignment and
Acceptance; and (b) agrees that it will, independently and without reliance upon
the Assignor, the Agent, or any other Lender and based on such documents and
information as it shall deem appropriate at the time, continue to make its own
credit and legal decisions in taking or not taking action under the Credit
Agreement.

         5.       Effective Date; Notices.

                  (a)      As between the Assignor and each Assignee, the
effective date for this Assignment and Acceptance shall be September 22, 2003
(the "EFFECTIVE DATE"); provided that the following conditions precedent have
been satisfied on or before the Effective Date:

                           (i)      this Assignment and Acceptance shall be
         executed and delivered by the Assignor, each Assignee, Borrowers, and
         Guarantors;

                           (ii)     the consent of the Agent (if necessary)
         required for an effective assignment of the Assigned Amount by the
         Assignor to the Assignee shall have been duly obtained and shall be in
         full force and effect as of the Effective Date; and

                           (iii)    each Assignee shall have complied with
         SECTION 11.2 of the Credit Agreement (if applicable).

         6.       Agent.

                  (a)      Each Assignee hereby appoints and authorizes the
Agent to take such action as agent on its behalf and to exercise such powers
under the Credit Agreement as are delegated to the Agent by the Lenders pursuant
to the terms of the Credit Agreement.

                  (b)      Each Assignee shall assume no duties or obligations
held by the Assignor in its capacity as Agent under the Credit Agreement.

         7.       Withholding Tax.

                  Each Assignee (a) represents and warrants to the Agent and the
Borrowers that under applicable law and treaties no tax will be required to be
withheld by the Agent or the Borrowers with respect to any payments to be made
to each Assignee hereunder, (b) agrees to furnish (if it is organized under the
laws of any jurisdiction other than the United States or any State thereof) to
the Agent and the

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       5

<PAGE>

Borrowers prior to the time that the Agent or the Borrowers is required to make
any payment of principal, interest, or fees in respect of the interest assigned
hereunder, duplicate executed originals of either U.S. Internal Revenue Service
Form W-8ECI or U.S. Internal Revenue Service Form W-8BEN (wherein each Assignee
claims entitlement to the benefits of a tax treaty that provides for a complete
exemption from U.S. federal income withholding tax on all payments hereunder)
and agrees to provide new Forms W-8ECI or W-8BEN upon the expiration of any
previously delivered form or comparable statements in accordance with applicable
U.S. law and regulations and amendments thereto, duly executed and completed by
the Assignee, and (c) agrees to comply with all applicable U.S. laws and
regulations with regard to such withholding tax exemption.

         8.       Representations and Warranties.

                  (a)      The Assignor represents and warrants that (i) it is
the legal and beneficial owner of the interest being assigned by it hereunder
and that such interest is free and clear of any Lien or other adverse claim;
(ii) it is duly organized and existing and it has the full power and authority
to take, and has taken, all action necessary to execute and deliver this
Assignment and Acceptance and any other documents required or permitted to be
executed or delivered by it in connection with this Assignment and Acceptance
and to fulfill its obligations hereunder; (iii) no notices to, or consents,
authorizations, or approvals of, any Person are required (other than any already
given or obtained) for its due execution, delivery, and performance of this
Assignment and Acceptance, and apart from any agreements or undertakings or
filings required by the Credit Agreement, no further action by, or notice to, or
filing with, any Person is required of it for such execution, delivery, or
performance; and (iv) this Assignment and Acceptance has been duly executed and
delivered by it and constitutes the legal, valid, and binding obligation of the
Assignor, enforceable against the Assignor in accordance with the terms hereof,
subject, as to enforcement, to bankruptcy, insolvency, moratorium,
reorganization, and other laws of general application relating to or affecting
creditors' rights and to general equitable principles.

                  (b)      The Assignor makes no representation or warranty and
assumes no responsibility with respect to any statements, warranties, or
representations made in or in connection with the Credit Agreement or the
execution, legality, validity, enforceability, genuineness, sufficiency, or
value of the Credit Agreement or any other instrument or document furnished
pursuant thereto. The Assignor makes no representation or warranty in connection
with, and assumes no responsibility with respect to, the solvency, financial
condition, or statements of the Loan Parties, or the performance or observance
by any Loan Party of any of its respective obligations under the Credit
Agreement or any other instrument or document furnished in connection therewith.

                  (c)      Each Assignee represents and warrants that (i) it is
duly organized and existing and it has full power and authority to take, and has
taken, all action necessary to execute and deliver this Assignment and
Acceptance and any other documents required or permitted to be executed or
delivered by it in connection with this Assignment and Acceptance, and to
fulfill its obligations hereunder; (ii) no notices to, or consents,
authorizations, or approvals of, any Person are required (other than any already
given or obtained) for its due execution, delivery, and performance of this
Assignment and Acceptance; and apart from any agreements or undertakings or
filings required by the Credit Agreement, no further action by, or notice to, or
filing with, any Person is required of it for such execution, delivery, or
performance; (iii) this Assignment and Acceptance has been duly executed and
delivered by it and constitutes the legal, valid, and binding obligation of each
Assignee, enforceable against each Assignee in accordance with the terms hereof,
subject, as to enforcement, to bankruptcy, insolvency, moratorium,
reorganization, and other laws of general application relating to or affecting
creditors' rights and to general equitable principles; and (iv) it is an
Eligible Assignee.

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       6

<PAGE>

                  (d)      Each Borrower and Guarantor represents and warrants
that after giving effect to the execution and delivery of this Assignment and
Acceptance and the consummation of the transactions contemplated hereby, and
with this Assignment and Acceptance constituting one of the Loan Documents, the
representations and warranties set forth in ARTICLE 6 of the Credit Agreement
are true and correct on the date hereof as though made on and as of such date,
and no Default or Event of Default has occurred and is continuing as of the date
hereof. Execution by any Borrower of this Assignment and Acceptance shall also
constitute its consent hereto as a Guarantor.

         9.       Further Assurances.

                  The Assignor and Assignees each hereby agrees to execute and
deliver such other instruments, and take such other action, as either party may
reasonably request in connection with the transactions contemplated by this
Assignment and Acceptance, including the delivery of any notices or other
documents or instruments to the Borrowers or the Agent, which may be required in
connection with the assignment and assumption contemplated hereby.

         10.      Miscellaneous.

                  (a)      Borrowers and Guarantors hereby acknowledge and agree
that all of their obligations under the Credit Agreement, as amended hereby, and
the other Loan Documents, shall remain in full force and effect following the
execution and delivery of this Assignment and Acceptance and such obligations
are hereby affirmed, ratified, and confirmed by Borrowers and Guarantors.

                  (b)      Any amendment or waiver of any provision of this
Assignment and Acceptance shall be in writing and signed by the parties hereto.
No failure or delay by either party hereto in exercising any right, power, or
privilege hereunder shall operate as a waiver thereof and any waiver of any
breach of the provisions of this Assignment and Acceptance shall be without
prejudice to any rights with respect to any other or further breach thereof.

                  (c)      All payments made hereunder shall be made without any
set-off or counterclaim.

                  (d)      Each Assignee shall pay its own costs and expenses
incurred in connection with the negotiation, preparation, execution, and
performance of this Assignment and Acceptance and the Loan Parties shall pay
such costs and expenses of the Assignor.

                  (e)      This Assignment and Acceptance may be executed in any
number of counterparts and all of such counterparts taken together shall be
deemed to constitute one and the same instrument.

                  (f)      THIS ASSIGNMENT AND ACCEPTANCE SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE LAW OF THE STATE OF NEW YORK. The Assignor
and Assignees each irrevocably submits to the non-exclusive jurisdiction of any
State or Federal court sitting in New York over any suit, action, or proceeding
arising out of or relating to this Assignment and Acceptance and irrevocably
agrees that all claims in respect of such action or proceeding may be heard and
determined in such New York State or Federal court. Each party to this
Assignment and Acceptance hereby irrevocably waives, to the fullest extent it
may effectively do so, the defense of an inconvenient forum to the maintenance
of such action or proceeding.

                  (g)      THE ASSIGNOR AND ASSIGNEES EACH HEREBY KNOWINGLY,
VOLUNTARILY, AND INTENTIONALLY WAIVES ANY RIGHTS IT MAY HAVE TO A TRIAL

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       7

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BY JURY IN RESPECT OF ANY LITIGATION BASED HEREON, OR ARISING OUT OF, UNDER, OR
IN CONNECTION WITH THIS ASSIGNMENT AND ACCEPTANCE, THE CREDIT AGREEMENT, ANY
RELATED DOCUMENTS AND AGREEMENTS, OR ANY COURSE OF CONDUCT, COURSE OF DEALING,
OR STATEMENTS (WHETHER ORAL OR WRITTEN).

                  IN WITNESS WHEREOF, the Assignor and each Assignee have caused
this Assignment and Acceptance to be executed and delivered by their duly
authorized officers as of the date first above written.

                    [REMAINDER OF PAGE INTENTIONALLY BLANK;
                            SIGNATURE PAGES FOLLOW.]

                                  AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

                                       8

<PAGE>

ASSIGNOR:                           BANK OF AMERICA, N.A.,
                                    as a Lender

                                    By: /s/ Robert Mostert
                                        ----------------------------------------
                                        Name: Robert Mostert
                                        Title: Vice President

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT

<PAGE>

Consent and Acceptance:             BANK OF AMERICA, N.A.,
                                    as Agent

                                    By: /s/ Robert Mostert
                                        ----------------------------------------
                                        Name: Robert Mostert
                                        Title: Vice President

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

Borrower Consent and Acceptance:

                                      WESTLAKE CHEMICAL CORPORATION, a Delaware
                                      corporation

                                      WESTLAKE PVC CORPORATION, a Delaware
                                      corporation

                                      WESTLAKE VINYLS, INC., a Delaware
                                      corporation

                                      By:  /s/ Albert Chao
                                           -------------------------------------
                                           Albert Chao
                                           President of the above Borrowers

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT


<PAGE>

Borrower Consent and Acceptance:

                             NORTH AMERICAN PIPE CORPORATION, a Delaware
                             corporation

                             VAN BUREN PIPE CORPORATION, a Delaware corporation

                             WESTECH BUILDING PRODUCTS, INC., a Delaware
                             corporation

                             By:  /s/ John A. Labuda
                                  --------------------------------------
                                   John A. Labuda
                                   President of the above Borrowers

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

Borrower Consent and Acceptance:

                            GEISMER VINYLS COMPANY LP, a Delaware limited
                            partnership
                                By: GVGP, Inc., its general partner

                            WESTLAKE PETROCHEMICALS LP, a Delaware limited
                            partnership
                                By: Westlake Chemical Investments, Inc.,
                                    its general partner

                            WESTLAKE POLYMERS LP, a Delaware limited partnership
                                By: Westlake Chemical Investments, Inc.,
                                    its general partner

                            WESTLAKE STYRENE LP, a Delaware limited partnership
                                By: Westlake Chemical Holdings, Inc.,
                                    its general partner

                            WPT LP, a Delaware limited partnership
                                By: Westlake Chemical Holdings, Inc.,
                                    its general partner

                                By: /s/ Albert Chao
                                    ------------------------------------
                                    Albert Chao
                                    President of the general partners of
                                       the above Borrowers

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

The undersigned jointly and severally consent and agree to the execution and
delivery of the Assignment and Acceptance.

                                 GRAMERCY CHLOR-ALKALI CORPORATION, a
                                 Delaware corporation
                                 GVGP, INC. , a Delaware corporation
                                 WESTLAKE CHEMICAL HOLDINGS, INC. ,
                                 a Delaware corporation
                                 WESTLAKE CHEMICAL INVESTMENTS, INC. , a
                                 Delaware corporation
                                 WESTLAKE MANAGEMENT SERVICES, INC. , a
                                 Delaware corporation
                                 WESTLAKE OLEFINS CORPORATION, a Delaware
                                 corporation
                                 WESTLAKE OVERSEAS CORPORATION, a United States
                                 Virgin Islands corporation
                                 WESTLAKE RESOURCES CORPORATION, a Delaware
                                 corporation
                                 WESTLAKE VINYL CORPORATION, a Delaware
                                 corporation

                                 By:  /s/ Albert Chao
                                      ------------------------------------------
                                      Albert Chao
                                      President of the above entities

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

The undersigned jointly and severally consent and agree to the execution and
delivery of the Assignment and Acceptance.

                                 NORTH AMERICAN PROFILES, INC. , a Delaware
                                 corporation

                                 By:   /s/ John A. Labuda
                                       -----------------------------------------
                                       John A. Labuda
                                       President

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

The undersigned jointly and severally consent and agree to the execution and
delivery of the Assignment and Acceptance.

                                 GEISMAR HOLDINGS, INC. , a Delaware corporation
                                 WESTLAKE CHEMICAL MANUFACTURING, INC. ,
                                 a Delaware corporation
                                 WESTLAKE CHEMICAL PRODUCTS, INC. , a Delaware
                                 corporation
                                 WESTLAKE DEVELOPMENT CORPORATION, a
                                 Delaware corporation

                                 By:  /s/ R. Michael Looney
                                      ------------------------------------------
                                       R. Michael Looney
                                       President of the above entities

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                           GENERAL ELECTRIC CAPITAL CORPORATION,
                                    as a Lender

                                    By: /s/ John Hanley
                                        ----------------------------------------
                                        Name:  John Hanley
                                        Title: Duly Authorized Signatory

Assigned Interest to this Assignee:  13.750%

<TABLE>
<CAPTION>
REVOLVING COMMITMENT ASSIGNED          OUTSTANDING L/C OBLIGATIONS
-----------------------------          ---------------------------
<S>                                    <C>
       $27,500,000                            $1,993,794.34
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT




<PAGE>

ASSIGNEE:                           THE CIT GROUP/BUSINESS CREDIT, INC.,
                                    as a Lender

                                    By: /s/ Richard D. Hatlsy Jr.
                                        ----------------------------------------
                                        Name:  Richard D. Hatlsy Jr.
                                        Title: VP Underwriting Mgr.

Assigned Interest to this Assignee:  13.750%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$27,500,000                        $ 1,993,794.34
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT




<PAGE>

ASSIGNEE:                     PNC BANK, NATIONAL ASSOCIATION,
                              as a Lender

                              By:  /s/ Paul R. Frank
                                   ---------------------------------------------
                                  Name:  Paul R. Frank
                                  Title: Vice President, Relationship Manager

Assigned Interest to this Assignee:  12.500%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ----------------
<S>                                <C>
 $25,000,000                        $1,812,540.31
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                         WELLS FARGO FOOTHILL, LLC,
                                  as a Lender

                                  By:  /s/ Sanat Amladi
                                      ------------------------------------------
                                      Name:  Sanat Amladi
                                      Title: Vice President

Assigned Interest to this Assignee:  12.500%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$25,000,000                        $ 1,812,540.31
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                         LASALLE BUSINESS CREDIT, LLC
                                  as a Lender

                                  By:  /s/ Joseph G. Frdacz
                                       -----------------------------------------
                                      Name:  Joseph G. Frdacz
                                      Title: SR VP

Assigned Interest to this Assignee:  11.250%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$22,500,000                        $ 1,631,286.28
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                         UBS AG, STAMFORD BRANCH,
                                  as a Lender

                                  By:  /s/ Wilfred V. Saint
                                       -----------------------------------------
                                      Name:  Wilfred V. Saint
                                      Title: Associate Director
                                               Banking Products Services, US

                                  By:  /s/ Luke Goldsworthy
                                       -----------------------------------------
                                      Name:  Luke Goldsworthy
                                      Title: Associate Director
                                             Banking Products Services, US

Assigned Interest to this Assignee:  8.750%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$17,500,000                        $ 1,268,778.22
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                         CREDIT SUISSE FIRST BOSTON, ACTING THROUGH
                                  ITS CAYMAN ISLANDS BRANCH,
                                  as a Lender

                                  By:  /s/ S. William Fox
                                       -----------------------------------------
                                      Name:  S. William Fox
                                      Title: Director

Assigned Interest to this Assignee:  5.000%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$ 10,000,000                       $  725,016.13
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

ASSIGNEE:                         DEUTSCHE BANK TRUST COMPANY AMERICAS,
                                  as a Lender

                                  By:  /s/ Kevin F. Sullivan
                                       -----------------------------------------
                                      Name:  Kevin F. Sullivan
                                      Title: MD

Assigned Interest to this Assignee:  5.000%

<TABLE>
<CAPTION>
 REVOLVING
COMMITMENT                         OUTSTANDING L/C
 ASSIGNED                            OBLIGATIONS
----------                         ---------------
<S>                                <C>
$10,000,000                        $  725,016.13
</TABLE>

Effective Date:            September 22, 2003

                               SIGNATURE PAGE TO
                 AMENDMENT, ASSIGNMENT AND ACCEPTANCE AGREEMENT
<PAGE>

                                  SCHEDULE 1.2

                              LENDERS' COMMITMENTS
<TABLE>
<CAPTION>
================================================== =========================== ========================
                                                      REVOLVING LOAN                PRO RATA SHARE
                     LENDER                            COMMITMENT                    (3 DECIMALS)
================================================== =========================== ========================
<S>                                                   <C>                           <C>
Bank of America, N.A.                                   $35,000,000                  17.500%
-------------------------------------------------- ------------------------ ------------------------
General Electric Capital Corporation                    $27,500,000                  13.750%
-------------------------------------------------- ------------------------ ------------------------
The CIT Group/Business Credit, Inc.                     $27,500,000                  13.750%
-------------------------------------------------- ------------------------ ------------------------
PNC Bank, National Association                          $25,000,000                  12.500%
-------------------------------------------------- ------------------------ ------------------------
Wells Fargo Foothill, LLC                               $25,000,000                  12.500%
-------------------------------------------------- ------------------------ ------------------------
LaSalle Business Credit, LLC                            $22,500,000                  11.250%
-------------------------------------------------- ------------------------ ------------------------
UBS AG, Stamford Branch                                 $17,500,000                   8.750%
-------------------------------------------------- ------------------------ ------------------------
Credit Suisse First Boston, acting through its          $10,000,000                   5.000%
Cayman Islands Branch
-------------------------------------------------- ------------------------ ------------------------
Deutsche Bank Trust Company Americas                    $10,000,000                   5.000%
-------------------------------------------------- ------------------------ ------------------------
                                                          TOTAL                     100.000%
================================================== =========================== ========================
</TABLE>

                                                                    SCHEDULE 1.2