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

of the Securities Exchange Act of 1934

For the month of December, 2018

Commission File Number 1-15106

PETRÓLEO BRASILEIRO S.A.—PETROBRAS

(Exact name of registrant as specified in its charter)

Brazilian Petroleum Corporation—PETROBRAS

(Translation of Registrant’s name into English)

Avenida República do Chile, 65

20031-912 - Rio de Janeiro, RJ

Federative Republic of Brazil

(Address of principal executive office)

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

Form 20-F  ☒            Form 40-F  ☐

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  ☐            No  ☒

Sale of onshore fields - Lagoa Parda Cluster

Start of the non-binding phase

Rio de Janeiro, December 10, 2018 – Petróleo Brasileiro S.A. – Petrobras, further to the material fact of 10/08/2018, announces the beginning of the non-binding phase related to the sale of its entire equity share in three onshore production fields (Lagoa Parda, Lagoa Parda Norte and Lagoa Piabanha), located in the state of Espĺrito Santo, Brazil, jointly designated as Lagoa Parda Cluster.

At this stage of the project, the interested parties qualified in the previous phase will receive instructions on the divestment process, including guidelines for the elaboration and submission of non-binding proposals, and access to a virtual data room containing more information about the cluster.

This disclosure to the market complies with Petrobras’ divestment methodology and is aligned with the provisions of the special procedure for the sale of exploration, development and production of oil, natural gas and other fluid hydrocarbons, provided for in Decree 9.355/2018.

www.petrobras.com.br/ir

Contacts:

PETRÓLEO BRASILEIRO S.A. – PETROBRAS | Investor Relations Department | e-mail: petroinvest@petrobras.com.br

Av. República do Chile, 65 – 10th floor, 1002 – B – 20031-912 – Rio de Janeiro, RJ | Phone: 55 (21) 3224-1510 / 3224-9947

FORWARD-LOOKING STATEMENTS

This release includes forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, that are subject to risks and uncertainties. The forward-looking statements, which address the Company’s expected business and financial performance, among other matters, contain words such as “believe,” “expect,” “estimate,” “anticipate,” “optimistic,” “intend,” “plan,” “aim,” “will,” “may,” “should,” “could,” “would,” “likely,” and similar expressions. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date on which they are made. There is no assurance that the expected events, trends or results will actually occur. We undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information or future events or for any other reason.

The Company’s actual results could differ materially from those expressed or forecast in any forward-looking statements as a result of a variety of assumptions and factors. These factors include, but are not limited to, the following: (i) failure to comply with laws or regulations, including fraudulent activity, corruption, and bribery; (ii) the outcome of ongoing corruption investigations and any new facts or information that may arise in relation to the “Lava Jato Operation”; (iii) the effectiveness of the Company’s risk management policies and procedures, including operational risk; and (iv) litigation, such as class actions or proceedings brought by governmental and regulatory agencies. A description of other factors can be found in the Company’s Annual Report on Form 20-F for the year ended December 31, 2017, and the Company’s other filings with the U.S. Securities and Exchange Commission.

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.

Date: December 10, 2018.