"All company units are functioning normally, production and operational and employee safety were unaffected by the movement," Petrobras said in a statement on the strike which began late Sunday.
The FUP oil workers' union said earlier Monday that the work stoppage had interrupted production at Petrobras's 60,000 barrel-per-day P-34 platform in the Campos basin and that workers had stopped work at terminals and refineries nationwide.
The company said it remained open to negotiations to resolve the impasse with the oil workers' union, which began a five-day strike on Sunday night over a bigger share of company profits for workers and better working conditions.
Strike coordinator Joao Antonio de Moraes said strikers had also interrupted operations at a Petrobras a fuel terminal at the country's main international airport in Guarulhos and oil refineries.
An airport spokeswoman said jet fuel supplies had not been affected.
"Participation is very strong. We stopped P-34 and the Suape terminals in Pernambuco, the Solimoes terminal in Amazonas state and the Guarulhos terminal in greater Sao Paulo," de Moraes said, adding that strikers had committed to not allow service stations to run dry.
Traders shrugged off news of the strike, which began on Sunday night. The company's shares were up 5 percent at 30.57 reais in intraday trade on Monday at the Sao Paulo Stock Exchange.
Oil was trading more than $1.4 higher at nearly $53.50 a barrel, supported by a rise in the stock market boosted by strong housing data and a U.S. plan to remove toxic assets from bank balance sheets.
Petrobras is the largest publicly-traded oil company in Latin America. Its Brazilian crude output stood at a record 1.94 million barrels per day on average in February and the firm discovered potentially huge sub-salt reserves deep below the sea bed in 2007.
The FUP held a previous strike last July which succeeded in briefly reducing crude production on the first day, but Petrobras dispatched emergency crews who restored output within hours. The strike dragged on for several more days but with little or no effect on operations.
The union said it is planning a five-day stoppage and said it would review then whether to continue or call off the industrial action.
