Tensions are high in Brazil ahead of the auction of exploration rights of the Libra offshore oil near Rio de Janeiro.
More than 1,000 troops will stand guard outside the hotel where the sell-off will take place.
Workers at the state run oil company Petrobras have been on strike since Thursday in protest at the sale.
They also briefly occupied Brazil’s mines and energy ministry in Brasilia in protest.
The Libra field holds an estimated eight billion to 12 billion barrels of recoverable oil, according to both Brazil’s oil regulator and Dallas-based oil-reserve certification company Degolyer & MacNaughton.
If the projection holds up, Libra could nearly double Brazil’s oil reserves or have enough oil to supply the world’s crude demand for as much as 19 weeks.
Opposition to the sale of Libra is strong among Petrobras unions. The unions remain amgry about the 1997 end of Petrobras’ monopoly over exploration, production and refining and regularly attack any non-Petrobras involvement in oil production, whether the involvement is domestic or foreign.
The union’s nationalist sentiment is widely shared in Brazil. The creation of Petrobras 60 years ago this month is still considered by many, especially older Brazilians, as an act of national liberation.