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____

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Announcement of Relevant Equity Interest

Rio de Janeiro, December 15 2009 – Petróleo Brasileiro S/A - Petrobras announces that as a result of the merger of BlackRock, Inc. (BlackRock) and Barclays Global Investors, which took place on December 1 2009, BlackRock's aggregated equity interest reached approximately 6.16% of the preferred shares issued by Petrobras.

Aiming to comply with the provisions set forth by Article 12 of Comissão de Valores Mobiliários – CVM (Brazilian Securities and Exchange Commission) Instruction No. 358, dated to January 03 2002, Petrobras announces that:

I. BlackRock's registered head office is located at: 40 East 52^nd Street, New York, New York, 10022-5911, United States of America;

II. the aggregated equity stake held by BlackRock reached 98,489,963 preferred shares and 64,776,037 American Depositary Receipts (ADRs), equivalent to preferred shares issued by Petrobras;

III. the purpose of the mentioned equity stake is strictly one of investment; there is no intent to change the shareholding control or the administrative structure of Petrobras;

IV. BlackRock holds no debentures convertible into stock issued by Petrobras;

V. BlackRock has not signed any contracts or agreements that regulate the exercise of the right to vote or the purchase and sale of securities issued by Petrobras.

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www.petrobras.com.br/ri/english
Contacts: PETRÓLEO BRASILEIRO S. A. – PETROBRAS
Investor Relations Department | E-mail: petroinvest@petrobras.com.br / acionistas@petrobras.com.br
Av. República do Chile, 65 – 22^nd floor - 20031-912 - Rio de Janeiro, RJ | Tel.: 55 (21) 3224-1510 / 9947

This document 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 merely reflect the expectations of the Company’s management. Such terms as “anticipate”, “believe”, “expect”, “forecast”, “intend”, “plan”, “project”, “seek”, “should”, along with similar or analogous expressions, are used to identify such forecasts. These predictions evidently involve risks and uncertainties, whether foreseen or not by the Company. Therefore, the future results of operations may differ from current expectations, and readers must not base their expectations exclusively on the information presented herein.

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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.

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