Two Brazilian maintenance workers died as a result of a toxic gas leak at an offshore oil rig operated by the state oil firm Petrobras. "The workers died when doing maintenance work on a drainage tank at the B-37 platform on the Marlim block in the Campos basin on Wednesday evening," said a Petrobras spokesman, adding that the workers were employees of Ultratec engineering firm. He said it was yet unclear how the leak had occurred and what gas caused the deaths. There were no other casualties and there was no damage to the platform. "The leak was stopped at the same moment on Wednesday. A Petrobras commission is investigating the case." Campos Basin accounts for nearly 80 percent of Brazil's overall crude oil output.