May 19 (Bloomberg) -- Petroleo Brasileiro SA, owner of the Western Hemisphere's largest oil discovery in three decades, passed Microsoft Corp. and Industrial & Commercial Bank of China Ltd. to become the world's sixth-largest company by market value.

Petrobras, as Brazil's state-controlled oil producer is known, climbed 3.8 percent to 50 reais, pushing its capitalization to 487.9 billion reais ($295.6 billion), according to data compiled by Bloomberg. Microsoft, which yesterday revived the possibility of purchasing Yahoo! Inc., fell 1.8 percent to $29.46, lowering its overall value to $274 billion.

ICBC's A shares listed in Shanghai rose 0.2 percent to 6.22 yuan. The market value of the world's largest bank is 2.02 trillion yuan ($289.3 billion).

Petrobras surged with other oil and metals companies as growth in developing countries such as China and India increased demand for raw materials. Six of the top 10 companies by market value are energy or mining companies, while three are from China.

``We're having a bull run in oil and commodities and these companies are riding that wave,'' said John Praveen, chief investment strategist at Prudential International Investments Advisers LLC in Newark, New Jersey, a unit of Prudential Financial Inc., which oversees $648 billion. Petrobras also is benefiting from its ``oil discoveries and the fact they almost have a monopoly on Brazilian oil.''

Value Quadruples

Petrobras, which has seen its market value quadruple since 2004, is worth 41 percent less than Exxon Mobil Corp., the world's largest company at $498.6 billion. Exxon added $1.69 to $94.36 today for its sixth straight increase. By overtaking Microsoft, Petrobras also becomes the third-largest company in the hemisphere after Exxon and General Electric Co., according to Bloomberg data.

It is worth more than the entire Santiago stock exchange in Chile and more than two-thirds of the $426 billion in equities on the Mexico City Stock Exchange.

The Tupi field, announced by Petrobras on Nov. 8, has 5 billion to 8 billion barrels of recoverable oil, the biggest discovery in the Americas since 1976, when the Cantarall field was found in the Gulf of Mexico. In January, Petrobras said its Jupiter field may hold as much oil and natural gas equivalent as Tupi.

A Brazilian regulator said the nearby Carioca field may have 33 billion barrels, though Petrobras declined to confirm if the estimate, based on a magazine article, was accurate.

To contact the reporter on this story: Jeb Blount in Rio de Janeiro at jblount@bloomberg.netAlexander Ragir in Rio de Janeiro at aragir@bloomberg.net

Last Updated: May 19, 2008 18:02 EDT