Bolsonaro told reporters that the crude oil "does not seem to come from an off-shore platform" and suggested it was from another country.
"It could be something criminal, it could be an accidental spill, it could also be a ship that sank".
Had the oil originated from a shipwreck, as Bolsonaro posited on Monday, it would still be seeping onto the beaches, he said. He declined to name the country because the investigation is still underway. Its origins remain unknown.
Speaking with lawmakers on Tuesday, Petrobras Chief Executive Roberto Castello Branco said the company had collected 133 tonnes (146.6 tons) of oil along Brazil's northeastern shoreline, adding the slicks were "strange" and "worrying".
After a one-month analysis of samples from the oil, Petrobras found that the oil is not of any type produced, transported or sold in Brazil, but a blend of Venezuelan oil.
After an investigation last month, Brazil's navy and the state-controlled oil company Petrobas concluded that the oil was produced overseas, but did not know where, Reuters reported.