A cause had not been determined, said BP spokesman Ronnie Chappell in Houston on Wednesday.
On Tuesday, after power was restored and crews were able to board the platform, information from data recorders was sent to the shore for analysis, Chappell said.
"It's a history of the status of the equipment and actions taken by the operators, prior to the evacuation," Chappell said. "It will also provide information on what happened on the vessel after the people were removed last week."
Thunder Horse, the largest platform in the Gulf of Mexico, is the centre of the Thunder Horse field, located about 240km southeast of New Orleans in about 1,800m of water.
Until the accident, BP expected it to begin producing oil - as much as 240,000 barrels per day - in late 2005. Exxon Mobil Corporation is a partner in the project.
"It's too early to say how this will impact the project's schedule," Chappell said on Wednesday.
Currently, the Gulf of Mexico produces about 1.5 million barrels of oil per day.
Evacuation due to Dennis
Thunder Horse was evacuated on Friday in anticipation of hurricane Dennis.
The listing platform was first noticed Monday by a passing ship.
"It's a history of the status of the equipment and actions taken by the operators, prior to the evacuation"
BP spokesman in Houston, USA
After that, BP and the Coast Guard set up a response centre in Morgan City, near the Louisiana coast.
BP and the Coast Guard both said there has been no evidence of pollution. Robots were used to examine the platform's hull, which showed no sign of damage, BP said.
Chappell would not speculate on how long it might take to right the platform, which was listing at about 20 degrees.
Ballast pumps aboard the platform are operational, he said, and additional pumps are being brought in.
The process of balancing the platform using water as ballast is similar to that used on ships, Chappell said.