Brazilian senators debated alternatives to a 2010 law that requires state-run oil firm Petrobras to take a minimum 30 percent stake in new development contracts and function as operator in Brazil's subsalt oil areas.
One option would be to give Petrobras the right of first refusal on such contracts but not require it to take a 30 percent stake, said Senator Eunicio Oliveira.
Oliveira said a vote was not expected on his proposal on Wednesday nor on a broader bill to change the law proposed by senator Jose Serra from the opposition PSDB party.
The current rules have been criticized for limiting foreign investment in the Subsalt Poligon, a region off Brazil's coast near Rio de Janeiro where large resources are trapped far beneath the seabed by a layer of mineral salts.
Petroleo Brasileiro SA, as the firm is formally known, is the world's most indebted oil company. It has said it may not have the financial strength to finance such areas, putting at risk oil development and the billions in royalties the government wants.
Serra is opposed to the right of first refusal option. Senate President Renan Calheiros wants to call a vote but lawmakers more closely aligned with President Dilma Rousseff have been trying to stall.
Rousseff's government opposes changes to the law.