A newly-tapped oil field off the coast of Brazil could contain up to 15 billion barrels of oil, officials say.
Brazil's national petroleum agency said the Libra field most probably held around 8 billion barrels.
That matches the size of the giant Tupi oil field, whose discovery in 2007 drew attention to Brazil's potential as a major oil producer.
If the 15 billion barrel figure were confirmed it would double Brazil's known oil reserves.
It would also be the biggest oil field discovered in the Americas since 1976, when Mexico found the giant Cantarell field in the Gulf of Mexico.
The Libra exploratory well is located 183km (114 miles) offshore from Rio de Janeiro.
"The volume of recoverable oil belonging to the nation could vary from 3.7 billion to 15 billion barrels, with the most likely estimate being 7.9 billion barrels," the national petroleum agency (ANP) said in a statement.
Brazil has discovered billions of barrels of oil in the last few years, mostly in deep, pre salt fields off its south-eastern coast.
The discoveries should make Brazil one of the world's top 10 oil producers.
Outgoing President Luiz Inacio Lula da Silva has said future oil revenues will be used to eradicate poverty and invest in education and technology.
In September the Brazilian oil company Petrobras, which is partly owned by the state, raised $70bn (£44.7bn) to develop the new fields in the world's largest ever public share offering.
BBC News
