An explosion from a suspected gas leak on a Petrobras rig off Brazil killed three people, injuring 10 and leaving six missing.
There were 74 workers on board.
The company, mired in a huge corruption scandal, said the situation is under control.
No oil was spilled, the state oil regulator, the National Petroleum Agency (ANP), said. The regulator has announced two separate investigations into the incident.
The rig operating in the area since 2009 had a daily average production of 2.25 million cubic metres of natural gas and 2,200 barrels of oil in December.
The rig explosion occurred at the FPSO Cidade de Sao Mateus - owned by Norwegian firm BW Offshore and leased by Petrobras - about 120 kilometres off the coast of the state of Espirito Santo.
The state health office said two people had suffered serious burns and eight had concussions, reports AFP.
The latest accident follows a string of recent accidents at refineries and rigs owned by Petrobras. Last month, an explosion at a refinery in the north-eastern state of Bahia wounded three people.
In February 2014, Petrobras partly evacuated an offshore rig that was tilting over.
In December 2013, a fire forced the shutdown of an oil rig after two workers were wounded. A week later, a refinery fire in Rio de Janeiro forced the company to temporarily close a production unit.
Petrobras is currently embroiled in a scandal involving kickbacks to politicians that led to the resignation of its board of directors last week.
Aldemir Bendine took over as chief executive from Graca Foster, who was forced to step down under market and political pressure.
Petrobras has also been hit hard by sliding oil prices, which fell 60 per cent between June and January.