国际英语新闻：BP releases report on spill investigation

The report also confirmed that the rig's blow-out prevent on the seabed failed to operate in the accident "probably because critical components were not working."

"It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy. Multiple parties, including BP, Halliburton and Transocean, were involved," said BP' s outgoing CEO Tony Hayward, who was heavily criticized for his handling of the crisis.

BP-leased Deepwater Horizon drilling rig exploded off the Louisiana coast in late April, killing 11 workers and unleashing the worst spill in U.S. history, with millions of gallons of oil gushing into the Gulf of Mexico from the ruptured underwater well.