May 15 (Bloomberg) -- Petroleo Brasileiro SA, Brazil's state-controlled oil company, has drilled halfway through its offshore Carioca deposit and will need more time to determine its size, Mines and Energy Minister Edison Lobao said.

Carioca is part of Brazil's new pre-salt region, an oil district beneath as much as 2,000 meters (6,500 feet) of water and as much as 4,000 meters of seabed. It's also home to the Tupi field, which holds as much as 8 billion barrels of oil and is the largest Western Hemisphere oil discovery in three decades, Lobao said today in an interview in his office in Brasilia.

Only 15 wells have been drilled in the pre-salt region by Petrobras, as the Rio de Janeiro-based company is known, and by rivals such as Irving, Texas-based Exxon Mobil Corp. and Royal Dutch Shell Plc, Lobao said. Brazil will need more wells and at least a year to get a good picture of the entire pre-salt region, he said.

To contact the reporters on this story: Jeb Blount in Rio de Janeiro at jblount@bloomberg.net; Carla Simoes in Brasilia at csimoes1@bloomberg.net

Last Updated: May 15, 2008 12:57 EDT