Updated

WASHINGTON (AP) — The CEO of the company that owned the oil drilling rig that exploded in the Gulf of Mexico says the accident was caused by a failure of its cementing, casing or perhaps both.

Transocean Ltd. CEO Steven Newman said at a Senate hearing Tuesday that the April 20 explosion of the Deepwater Horizon rig was unusual because it happened after construction of the well was essentially complete.

He said that the explosion that killed 11 workers could not have happened unless the cement, well casing — or both of those elements — failed. The rig sank and has been gushing oil into the Gulf.

Newman dismissed suggestions that a blowout preventer owned by Transocean may have been a cause.