Exhibit 10.4

REVOLVER CREDIT AGREEMENT

SIXTH AMENDMENT TO CREDIT AGREEMENT

This SIXTH AMENDMENT TO CREDIT AGREEMENT (this “Amendment”) is entered into as
of March     , 2006, among WESTLAKE CHEMICAL CORPORATION (“Westlake”) and
certain of its domestic subsidiaries listed as Borrowers to the Credit Agreement
described below (collectively, the “Borrowers”), Lenders under the Credit
Agreement, BANK OF AMERICA, N.A., in its capacity as Agent for Lenders under the
Credit Agreement (the “Agent”), and Guarantors under the Credit Agreement
(hereinafter defined).

Reference is made to the Credit Agreement, dated as of July 31, 2003 (as
amended, modified, and supplemented, the “Credit Agreement”), among the
Borrowers, the Agent, and Lenders party thereto. Unless otherwise defined in
this Amendment, capitalized terms used herein shall have the meanings set forth
in the Credit Agreement and all Section references herein are to Sections in the
Credit Agreement.

RECITALS

A. Borrowers have requested that Lenders agree to amend certain provisions of
the Credit Agreement, including without limitation, amending certain covenants
and increasing the Maximum Inventory Loan Amount.

B. Subject to the terms and conditions of this Amendment, Lenders are willing to
agree to such amendments.

Accordingly, for adequate and sufficient consideration, the parties hereto
agree, as follows:

Paragraph 1. Amendments to Credit Agreement. By execution of this Amendment, the
Credit Agreement is hereby amended as follows:

1.1 December Financial Reports. The first sentence of Section 5.2(c) of the
Credit Agreement is amended in its entirety to read as follows:

“(c) As soon as available, but in any event not later than thirty (30) days
after the end of each month other than March, June, September, or December (and,
as soon as available, but in any event not later than forty-five (45) days after
the end of each March, June, and September, and, as soon as available, but in
any event not later than the earlier of (i) the filing of Financial Statements
with the SEC pursuant to Section 5.2(a) and (ii) ninety (90) days after the end
of each December, and without duplication of the Financial Statements required
by Section 5.2(b)), consolidated unaudited balance sheets of Westlake and its
Subsidiaries as at the end of such month, and consolidated unaudited income
statements and cash flow statements for Westlake and its Subsidiaries for such
month and for the period from the beginning of the Fiscal Year to the end of
such month, all in reasonable detail, fairly presenting the financial position
and results of operations of Westlake and its Subsidiaries as at the date
thereof and for such periods, and prepared in accordance with GAAP (except for
the inclusion of necessary footnotes) applied consistently with the audited
Financial Statements required to be delivered pursuant to Section 5.2(a),
together with a schedule setting forth in reasonable detail the calculation of
the Fixed Charge Coverage Ratio for the immediately preceding twelve (12) month
period.”

 

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1.2 Accounts Receivable Reporting. Section 5.2(l) of the Credit Agreement is
amended in its entirety to read as follows:

“ (l) As soon as available, but in any event by the second Business Day of each
week for the prior week ending on the last Business Day of such prior week;
provided that not more than four (4) times in any fiscal year, the following may
be delivered by the third Business Day of such week, in form and substance
reasonably satisfactory to the Agent: (i) a schedule of each Loan Party’s
Accounts created, credit memoranda, and collections for the applicable week,
together with a reconciliation of each Loan Party’s Accounts created, credit
memos, collections and other adjustments to Accounts since the last such weekly
reconciliation and a Borrowing Base Certificate; (ii) a summary of each credit
memorandum in excess of $1,000,000; (iii) after the occurrence of the Account
Triggering Date, an Inventory report; and (iv) with the delivery of each of the
foregoing, a certificate executed by a Responsible Officer on behalf of all of
the Loan Parties certifying as to the accuracy and completeness of the
foregoing; provided that so long as the sum of Availability plus the
unrestricted cash of Westlake and its Subsidiaries (A) exceeds $200,000,000 or
(B) becomes less than $200,000,000 (during which time the reports and
information required to be delivered pursuant to this Section 5.2(l) shall be
delivered on a weekly basis as aforesaid) but thereafter exceeds $250,000,000
for a period of three consecutive months and continues to exceed $200,000,000
after the end of such three consecutive month period, the reports and other
information required to be delivered pursuant to this Section 5.2(l) shall be
required to be delivered as soon as available, but in any event within fifteen
(15) days after the end of each month or more frequently as requested by the
Agent to determine Availability or otherwise.”

1.3 Maximum Inventory Loan Amount. The definition of Maximum Inventory Loan
Amount in Annex A to the Credit Agreement is amended in its entirety to read as
follows:

"“Maximum Inventory Loan Amount” means $200,000,000.”

Paragraph 2. Amendments to Security Agreements. By execution of this Amendment,
each of the “$100,000,” “$250,000,” and “$500,000” amounts appearing in
Sections 11(b), (d) and (e) of each of the Security Agreements is amended to
read “$1,000,000.”

Paragraph 3. Effective Date. Notwithstanding any contrary provision, this
Amendment is not effective until the date (the “Effective Date”) upon which:

(a) the Agent has received counterparts of this Amendment executed by each
Borrower, each Guarantor, Agent, and each Lender;

(b) all representations and warranties made hereunder and in the other Loan
Documents shall be true and correct as of the date hereof as though made on and
as of the date hereof, other than any such representation or warranty which
relates to a specified prior date;

(c) No Default or Event of Default shall have occurred and be continuing; and

(d) Borrowers shall have paid Attorney Costs of the Agent incurred in connection
with the Loan Documents, including any outstanding Attorney Costs of the Agent
on the Effective Date.

Paragraph 4. Acknowledgment and Ratification. As a material inducement to the
Agent and Lenders to execute and deliver this Amendment, each Borrower and each
Guarantor (a) consent to the agreements in this Amendment; and (b) agree and
acknowledge that the execution, delivery, and performance of this Amendment
shall in no way release, diminish, impair, reduce, or otherwise affect the
respective obligations of Borrowers or Guarantors under their respective Loan
Documents, which Loan Documents shall remain in full force and effect, and all
Liens, guaranties, and rights thereunder are hereby ratified and confirmed.

 

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Paragraph 5. Representations. As a material inducement to Lenders to execute and
deliver this Amendment, each Borrower and each Guarantor represent and warrant
to Lenders (with the knowledge and intent that Lenders are relying upon the same
in entering into this Amendment) that as of the Effective Date and as of the
date of execution of this Amendment, (a) all representations and warranties in
the Loan Documents are true and correct in all material respects as though made
on the date hereof, except to the extent that (i) any of them speak to a
different specific date or (ii) the facts on which any of them were based have
been changed by transactions contemplated or permitted by the Credit Agreement,
(b) no Default or Event of Default exists, (c) the attachments to, and the
certifications made in, the Officer’s Certificates executed and delivered to the
Agent and Lenders in connection with the Fifth Amendment to the Credit Agreement
dated as of January 6, 2006, have not been modified or amended, remain in full
force and effect, and are hereby ratified and confirmed and (d) the execution,
delivery and performance of this Amendment have been duly authorized by all
necessary partnership and corporate action and this Amendment constitutes the
valid and binding obligation of each of them.

Paragraph 6. Fees and Expenses. Borrowers shall pay all reasonable costs, fees,
and expenses paid or incurred by the Agent in connection with this Amendment,
including, without limitation, Attorney Costs of the Agent in connection with
the negotiation, preparation, delivery, and execution of this Amendment and any
related documents.

Paragraph 7. Waiver. Each Loan Party (i) acknowledges and agrees that, as of the
date hereof, it has no actual or potential claim or cause of action against
Agent or any Lender relating to any Loan Documents or any actions or events
occurring on or before the date of this Amendment and (ii) waives and releases
any right to assert such claim or cause of action to the extent based on actions
or events occurring on or before the date hereof.

Paragraph 8. Miscellaneous.

8.1 This Amendment is a “Loan Document” referred to in the Credit Agreement, and
the provisions relating to Loan Documents in Article 13 of the Credit Agreement
are incorporated in this Amendment by reference. Unless stated otherwise (a) the
singular number includes the plural and vice versa and words of any gender
include each other gender, in each case, as appropriate, (b) headings and
captions may not be construed in interpreting provisions, (c) this Amendment
must be construed, and its performance enforced, under New York law, (d) if any
part of this Amendment is for any reason found to be unenforceable, all other
portions of it nevertheless remain enforceable, and (e) this Amendment may be
executed in any number of counterparts with the same effect as if all
signatories had signed the same document, and all of those counterparts must be
construed together to constitute the same document.

8.2 The Loan Documents shall remain unchanged and in full force and effect,
except as provided in this Amendment, and are hereby ratified and confirmed. On
and after the Effective Date, all references to the “Credit Agreement” shall be
to the Credit Agreement as herein amended. The execution, delivery, and
effectiveness of this Amendment shall not, except as expressly provided herein,
operate as a waiver of any rights of Lenders under any Loan Document, nor
constitute a waiver under any of the Loan Documents.

Paragraph 9. ENTIRE AGREEMENT. THIS AMENDMENT REPRESENTS THE FINAL AGREEMENT
BETWEEN THE PARTIES ABOUT THE SUBJECT MATTER OF THIS AMENDMENT AND MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE
PARTIES.

Paragraph 10. Parties. This Amendment binds and inures to Borrowers, Guarantors,
the Agent, Lenders, and their respective successors and assigns.

The parties hereto have executed this Amendment in multiple counterparts to be
effective as of the Effective Date.

Remainder of Page Intentionally Blank.

Signature Pages to Follow.

 

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

BANK OF AMERICA, N.A., as the Agent and a Lender

 

By:  

/s/ Robert Mostert

Name:   Robert Mostert Title:   Vice President

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

GENERAL ELECTRIC CAPITAL CORPORATION,

as a Lender

 

By:  

/s/ Bond Harberts

Name:   Bond Harberts Title:   Duly Authorized Signatory

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

THE CIT GROUP/BUSINESS CREDIT, INC.,

as a Lender

 

By:  

/s/ David Rothberg

Name:   David Rothberg Title:   Assistant Vice President

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

PNC BANK, NATIONAL ASSOCIATION,

as a Lender

 

By:  

/s/ Timothy S. Culver

Name:   Timothy S. Culver Title:   Vice President

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

WELLS FARGO FOOTHILL, LLC,

as a Lender

 

By:  

/s/ Juan Barrera

Name:   Juan Barrera Title:   Vice President

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

LASALLE BUSINESS CREDIT, LLC,

as a Lender

 

By:

 

/s/ Douglas Colletti

Name:   Douglas Colletti Title:   Senior Vice President

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

UBS AG, STAMFORD BRANCH,

as a Lender

 

By:  

/s/ Luis Pistecchia

Name:   Louis Pistecchia Title:   Director Banking Products Services, US By:  

/s/ Douglas Gervolino

Name:   Douglas Gervolino Title:  
Associated Director Banking Products Services, US

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

CREDIT SUISSE FIRST BOSTON, acting through

its Cayman Islands Branch, as a Lender

 

By:  

/s/ Alain Dacust

Name:   Alain Dacust Title:   Director By:  

/s/ Denise L. Alvarez

Name:   Denise L. Alvarez Title:   Associate

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

DEUTSCHE BANK TRUST COMPANY AMERICAS,

as a Lender

 

By:  

/s/ Marguerite Sutton

Name:   Marguerite Sutton Title:   Director By:  

/s/ Frank Fazio

Name:   Frank Fazio Title:   Director

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

 

  BORROWERS AND GUARANTORS:    

WESTLAKE CHEMICAL CORPORATION,

a Delaware corporation

   

WESTLAKE PVC CORPORATION,

a Delaware corporation

   

WESTLAKE VINYLS, INC.,

a Delaware corporation

   

NORTH AMERICAN BRISTOL CORPORATION,

a Delaware corporation

    By:  

/s/ Albert Chao

      Albert Chao       President of the above Borrowers

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

 

NORTH AMERICAN PIPE CORPORATION, a Delaware corporation

VAN BUREN PIPE CORPORATION,

a Delaware corporation

WESTECH BUILDING PRODUCTS, INC.,

a Delaware corporation

WESTECH PROFILES LIMITED,

a Delaware corporation

By:  

/s/ Wayne D. Morse

  Wayne D. Morse   President of the above Borrowers

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

 

WESTLAKE 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 Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

 

GUARANTORS: 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 RESOURCES CORPORATION, a
Delaware corporation WESTLAKE VINYL CORPORATION, a Delaware corporation WESTLAKE
INTERNATIONAL CORPORATION, a Delaware corporation WESTLAKE NG I CORPORATION, a
Delaware corporation WESTLAKE NG II CORPORATION a Delaware corporation By:  

/s/ Albert Chao

  Albert Chao   President of the above entities

 

Signature Page to Sixth Amendment

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Signature Page to that certain Sixth Amendment to Credit Agreement dated as of
the date first stated above, among Westlake Chemical Corporation and certain of
its domestic subsidiaries, as Borrowers, Bank of America, N.A., in its capacity
as Agent, Required Lenders, and Guarantors.

 

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 Sixth Amendment