French energy group Total said on Monday it had resigned from its role as operator of five exploration blocks in the Foz do Amazonas Basin, 120 kilometres offshore Brazil.
Some geologists have said the area may contain as many as 14 billion barrels of petroleum, more than the entire proven reserves of Mexico.
However environmentalists have tried to prevent oil exploration in the area, which is home to a sizeable reef.
"This decision opens a period of six months during which a new operator will be appointed, and to whom the operated activities will be handed over," Total said in a statement.
(Reporting by Maya Nikolaeva; Editing by Jan Harvey)
