A deepwater oil platform that burned for more than a day after a massive explosion sank into the Gulf of Mexico on Thursday, creating the potential for a major spill as it underscored the slim chances that the 11 workers still missing survived.

The sinking of the Deepwater Horizon, which burned violently until the gulf itself extinguished the fire, could unleash more than 300,000 of gallons of crude a day into the water. The environmental hazards would be greatest if the spill were to reach the Louisiana coast, some 50 miles away.