As filed with the Securities and Exchange Commission on July 29, 2014

Registration No. 333-195551

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 6

to

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Westlake Chemical Partners LP

(Exact Name of Registrant as Specified in Its Charter)

2801 Post Oak Boulevard, Suite 600

Houston, Texas 77056

(713) 960-9111

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

L. Benjamin Ederington

Vice President, General Counsel and Secretary

2801 Post Oak Boulevard, Suite 600

Houston, Texas 77056

(713) 960-9111

(Name, Address, Including Zip Code, and Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Approximate date of commencement of proposed sale to the public:

As soon as practicable after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box.  ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment that specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

Explanatory Note

This Amendment No. 6 is being filed solely for the purpose of filing an exhibit to the Registration Statement on Form S-1 (File No. 333-195551) and no changes or additions are being made hereby to the preliminary prospectus which forms a part of the Registration Statement or to Items 13, 14, 15 or 17 of Part II of the Registration Statement. Accordingly, the preliminary prospectus and Items 13, 14, 15 and 17 of Part II of the Registration Statement have been omitted from this filing.

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

See the Index to Exhibits on the page immediately preceding the exhibits for a list of exhibits filed as part of this registration statement on Form S-1, which Index to Exhibits is incorporated herein by reference.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Houston, State of Texas, on July 28, 2014.

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement has been signed below by the following persons in the capacities and the dates indicated.

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INDEX TO EXHIBITS

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