Petrobras said Tupi, which is offshore from Sao Paulo state in waters up to 3km deep, could produce up to eight billion barrels of light oil and natural gas.
The find - one of the biggest in the last two decades - could yet be followed by another discovery at a promising giant prospect still being explored farther south.
A follow-up discovery could place Brazil “among the countries with the biggest oil and gas reserves in the world”, according to Petrobras head, Jose Sergio Gabrielli.
Brazil’s total reserves could now place it “between Nigeria and Venezuela”, Gabrelli told a media conference in Rio de Janeiro.
Petrobras’ previous stated reserves, given at the end of 2006, were the equivalent of 11.46 billion barrels of oil.
The Tupi find alone could boost that by more than 60%.
Petrobras is one of the world’s leading deepwater explorers.
Petrobras operates the Tupi area, of which it holds 65%. British energy group BG holds a 25% share in the field and Portugal’s Petrogal-Galp Energia holds 10%.
