Brazilian police are investigating an oil spill in an offshore field operated by the US company Chevron.
Ships are working to disperse the slick 120km off the coast of Rio de Janeiro state.
The oil is leaking from a well in the Frade oil project, 370km off the Brazilian coast. Chevron says they have plugged the oil well, but the Brazilian government and police disagree.
Edison Lobao, Brazil's energy minister, has said the company will be "severely punished" if it is found to have failed in its environmental responsibilities.
In recent years Brazil has discovered huge oil reserves in the Atlantic.
Al Jazeera's Gabriel Elizondo reports from Rio de Janeiro.