UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

October 15, 2015

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:    x  Form 20-F     ¨  Form 40-F

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ¨

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934:    ¨  Yes    x  No

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): n/a

NEWS RELEASE

BHP BILLITON PRICES US$3.25 BILLION US DOLLAR HYBRID NOTES

BHP Billiton has priced US$3.25 billion of subordinated fixed rate reset notes in the US Dollar market across two tranches.

The issuance of these hybrid notes comprises:

Settlement of the notes is expected to occur on 19 October 2015, subject to customary closing conditions.

The proceeds will be used for general corporate purposes, which may include, without limitation, the repayment of existing debt of the BHP Billiton Group.

This announcement does not constitute an offer to sell, or the solicitation of an offer to buy, any securities in the United States, Canada, Japan, Australia or any other jurisdiction. The securities described herein have not been, and will not be, registered under the U.S. Securities Act of 1933, as amended or under any relevant securities laws of any state of the United States or any other jurisdiction, and may not be offered or sold in the United States or to any U.S. persons absent an effective registration statement covering such securities or an applicable exemption from such registration requirements.

Members of the BHP Billiton Group which is headquartered in Australia

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.