Brazil's National Petroleum Agency, known by its Portuguese initials ANP, told Bloomberg News a seep was reported by state-run oil producer Petroleo Brasileiro at its Rancador project off the Brazilian coast.
Within two days, ANP said it expected test results from the Rancador seep to determine the origin of the incident.
Chevron reported a similar incident at its Frade field last month. The project is about 230 miles off the coast of Rio de Janeiro in 3,800 feet of water.
The Brazilian government filed charges against Chevron and Transocean for the March seep and for the spill of more than 2,500 barrels of oil at the Frade field in November. Chevron said the incidents aren't related.
Brazil is also seeking to block Chevron from transferring its profits out of Brazil and halt operations at Frade.
An estimated 50 billion barrels of oil lies off the Brazilian coast, a volume that's expected to put the Latin American country on par with some of the world's top oil producers.