The world's largest offshore oil rig resumed sinking as rough seas impeded efforts to salvage it four days after blasts ripped through the structure, killing 10, the Brazilian owners said on Monday. After stabilizing the 40-story platform for a day and raising hopes it could be saved, the rig sank another 1.3 ft. (0.3 m) Sunday night and keeled over even further, Brazil's state oil giant Petrobras said. "There is still no estimate for how long it will take to stabilize the platform," a Petrobras spokesman said. Three explosions rocked the rig early last Thursday, killing 10 of the 175 men aboard and seriously injuring another. Petrobras, the biggest company in Brazil, was still trying to determine the cause of the explosions.