Just last September, the operator of the semisubmersible rig known as the Deepwater Horizon announced it had succeeded in drilling the deepest oil well in history. Operating in 4,130 feet (1,260 meters) of water, the rig had drilled six miles (10 km) beneath the sea floor to reveal a major petroleum find, the Tiber Prospect, for the giant oil company BP.

Now, authorities are trying to learn what went wrong on the platform, where an explosion left at least three people critically injured and 11 more missing as of Thursday. Rig operator Transocean Ltd. said 115 workers were evacuated safely, but the fire burned long after the blast, apparently fed by the flow of oil or gas hydrocarbons. The company