Helicopters and boats were scouring the Gulf for any sign of the workers who had not been accounted for.
Coast Guard Senior Chief Petty Officer Mike O'Berry said: "We're hoping everyone is in a life raft."
The rig was left tilting about 70 degrees and threatening to topple into the water.
It is owned by Transocean, based in Houston, and was under contract to BP. A BP spokesman said all its personnel were safe.
When the explosion happened the rig was drilling but was not in production.
Initial reports were as many as 12 missing, but the Coast Guard counted 98 survivors on two oil service boats and 17 injured, seven critically, who were taken to hospitals. Eleven were still unaccounted for at midday Wednesday, according to the Coast Guard.
Transocean spokesman Greg Panagos said it was too early to know what caused the accident.
He said: "Our focus right now is on taking care of the people." The 120-metre (396ft) long, semi-submersible Deepwater Horizon was still on fire hours after the explosion.
It was built in 2001 by Hyundai Heavy Industries Shipyard in South Korea and can accommodate a crew of up to 130.
Last year it set a world deepwater record when it drilled down over 10,700 metres (35,000ft) at another BP site in the Gulf of Mexico.
It is equipped with covered lifeboats with supplies to allow workers to survive for extended periods if they must evacuate.
Greg McCormack, director of the Petroleum Extension Service for the University of Texas at Austin,said: "The worst thing that can happen on an oil rig is you have a fire, and then you have to evacuate without the fire being put out, because then it can only get worse."