This month, Brazil’s government said it wanted the national oil company, Petrobras, to control all future development of the deep-sea fields discovered in 2007, which international geologists estimate could hold tens of billions of barrels of recoverable oil.

The change would make Petrobras the operator for the 62 percent of the new area that has yet to be bid out, consigning foreign companies to the role of financial investors. That would limit their ability to help set the pace for the oil fields’ development, while giving Petrobras significantly more power to generate jobs and award lucrative contracts.