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, 2011

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 ___X___ 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___X____

This report on Form 6-K is incorporated by reference in the Registration
Statement on Form F-3 of Petróleo Brasileiro -- Petrobras (No. 333-163665).

 

Declaration of Commerciality for Guará Area

            Rio de Janeiro, December 29, 2011 – Petróleo Brasileiro S.A. – Petrobras, as operator of the consortium of Block BM-S-9, informed that it submitted today the Declaration of Commerciality for the Guará area to the National Petroleum, Natural Gas and Biofuels Agency (ANP).

The new field will be called as Sapinhoá and the estimated total recoverable volume informed was 2.1 billion barrels of oil equivalent (boe). Sapinhoá is another giant field discovered in the Brazilian pre-salt layer and one of the biggest in the country, comprised of reservoirs with good quality oil (30º API).

            The consortium also submitted the final Evaluation Plan final report of the area. The Development Plan report will be submitted to the ANP in February 2012. The Declaration of Commerciality takes place following the execution of the Exploratory Evaluation Program in the area, which was conducted from the first drilled well in 2008.

Four wells were drilled in the area, including one to get data about the reservoir. In addition, four formation tests were conducted in three of the wells and a five-month extended well test (EWT) in the discovery well. The EWT confirmed the excellent productivity of the discovery well.  The flow was maintained throughout the entire test period and the test showed relevant information about the carbonate reservoirs for the optimization of the development plan.

            The Declaration of Commerciality for the field was anticipated by a year, considering that the deadline for the Evaluation Plan approved by the ANP was December 31, 2012.

            The exploratory success obtained in the area reaffirms the high potential of the pre-salt and signals a promising outlook for the Company’s output production growth and oil and natural gas reserves increase. Petrobras is the operator of Block BM-S-9, in partnership with BG Group (30%) and Repsol Sinopec Brasil (25%).

www.petrobras.com.br/ri

Para mais informações: PETRÓLEO BRASILEIRO S. A. – PETROBRAS

Relacionamento com Investidores I E-mail: petroinvest@petrobras.com.br / acionistas@petrobras.com.br

Av. República do Chile, 65 - 2202 - B - 20031-912 - Rio de Janeiro, RJI Tel.: 55 (21) 3224-1510 / 9947 I 0800-282-1540

Este documento pode conter previsões segundo o significado da Seção 27A da Lei de Valores Mobiliários de 1933, conforme alterada (Lei de Valores Mobiliários), e Seção 21E da lei de Negociação de Valores Mobiliários de 1934, conforme alterada (Lei de Negociação) que refletem apenas expectativas dos administradores da Companhia. Os termos “antecipa”, “acredita”, “espera”, “prevê”, “pretende”, “planeja”, “projeta”, “objetiva”, “deverá”, bem como outros termos similares, visam a identificar tais previsões, as quais, evidentemente, envolvem riscos ou incertezas previstos ou não pela Companhia. Portanto, os resultados futuros das operações da Companhia podem diferir das atuais expectativas, e o leitor não deve se basear exclusivamente nas informações aqui contidas.

 

 

www.petrobras.com.br/ri

Para mais informações: PETRÓLEO BRASILEIRO S. A. – PETROBRAS

Relacionamento com Investidores I E-mail: petroinvest@petrobras.com.br / acionistas@petrobras.com.br

Av. República do Chile, 65 - 2202 - B - 20031-912 - Rio de Janeiro, RJI Tel.: 55 (21) 3224-1510 / 9947 I 0800-282-1540

Este documento pode conter previsões segundo o significado da Seção 27A da Lei de Valores Mobiliários de 1933, conforme alterada (Lei de Valores Mobiliários), e Seção 21E da lei de Negociação de Valores Mobiliários de 1934, conforme alterada (Lei de Negociação) que refletem apenas expectativas dos administradores da Companhia. Os termos “antecipa”, “acredita”, “espera”, “prevê”, “pretende”, “planeja”, “projeta”, “objetiva”, “deverá”, bem como outros termos similares, visam a identificar tais previsões, as quais, evidentemente, envolvem riscos ou incertezas previstos ou não pela Companhia. Portanto, os resultados futuros das operações da Companhia podem diferir das atuais expectativas, e o leitor não deve se basear exclusivamente nas informações aqui contidas.

SIGNATURE

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 29, 2011

PETRÓLEO BRASILEIRO S.A--PETROBRAS
By:	/S/  Almir Guilherme Barbassa
	Almir Guilherme Barbassa Chief Financial Officer and Investor Relations Officer

FORWARD-LOOKING STATEMENTS

This press release may contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (Securities Act), and Section 21E of the Securities Exchange Act of 1934, as amended (Exchange Act) that are not based on historical facts and are not assurances of future results.  These forward-looking statements are based on management's current view and estimates of future economic circumstances, industry conditions, company performance and financial results. The words "anticipates", "believes", "estimates", "expects", "plans" and similar expressions, as they relate to the company, are intended to identify forward-looking statements. Statements regarding the declaration or payment of dividends, the implementation of principal operating and financing strategies and capital expenditure plans, the direction of future operations and the factors or trends affecting financial condition, liquidity or results o f operations are examples of forward-looking statements. Such statements reflect the current views of management and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, and operating factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations. 
All forward-looking statements are expressly qualified in their entirety by this cautionary statement, and you should not place reliance on any forward-looking statement contained in this press release. 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.