Oct. 3 (Bloomberg) -- Petroleo Brasileiro SA, Brazil's state-controlled oil company, and its partners in the Tupi field may spend as much as $50 billion to develop what is the biggest discovery in the Americas since 1976, according to Deloitte.

``It will be a challenge to finance these massive fields,'' Mauro Andrade, a Rio de Janeiro-based senior manager of Deloitte's Petroleum Services Group, said in an interview in London today. ``We are talking about ultra deepwater engineering. There is still a bit of a development risk involved, although the findings are really quite massive.''

Andrade estimates Tupi's recoverable oil reserves at 5 billion to 5.5 billion barrels, meaning development costs would be about $10 per barrel of oil equivalent, he said. Equipment modifications necessitated by deepwater pressure may increase the estimate for development costs, he said.

Petrobras said in November that Tupi may have as much as 8 billion barrels of oil, the largest find in the Americas since Mexico's Cantarell field was found in 1976. If confirmed, Tupi and the neighboring Iara find could almost double Brazil's 12.6 billion barrels of proven oil reserves, according to BP Plc.

Rio de Janeiro-based Petrobras is the operator and owns 65 percent of the block where both the Iara and Tupi wells were drilled. Reading, England-based BG Group Plc, the U.K.'s third- largest oil and natural-gas producer, owns 25 percent and Lisbon-based Galp Energia SGPS SA, Portugal's biggest oil company, owns 10 percent.

Iara and Tupi lie in a new petroleum province known as the pre-salt area, which runs 800 kilometers (500 miles) along Brazil's coast from Espirito Santo to Santa Catarina states. The province has oil deposits beneath a layer of salt resting as much as 3,000 meters beneath the ocean surface and another 3,000 to 5,000 meters below the seabed.

Development of the fields and surrounding discoveries will cost about $600 billion, according to UBS AG, a Swiss bank. Once the Brazilian government decides on a new regulatory framework for oil exploration, more blocks in the pre-salt area may be auctioned, Deloitte's Andrade said today.

To contact the reporter on this story: Joao Lima in Lisbon at jlima1@bloomberg.net; Eduard Gismatullin in London at egismatullin@bloomberg.net.

Last Updated: October 3, 2008 08:53 EDT