Officials initially seemed to underestimate the threat of a leak, just as BP did last year when it told the government such an event was highly unlikely. Rear Adm. Mary E. Landry, the chief Coast Guard official in charge of the response, said on April 22, after the rig sank, that the oil that was on the surface appeared to be merely residual oil from the fire, though she said it was unclear what was going on underwater. The day after, officials said that it appeared the well’s blowout preventer had kicked in and that there did not seem to be any oil leaking from the well, though they cautioned it was not a guarantee.

BP officials, even after the oil leak was confirmed by using remote-controlled robots, expressed confidence that the leak was slow enough, and steps taken out in the Gulf of Mexico aggressive enough, that the oil would never reach the coast.

(The NOAA document on a potentially far larger leak, first obtained by The Press-Register in Mobile, Ala., was described by an agency spokesman as simply a possibility raised by a staff member, not an official prediction.)

Some oil industry critics questioned whether the federal government is too reliant on oil companies to manage the response to major spills, leaving the government unable to evaluate if the response is robust enough.

Image In this photo released by Greenpeace, a boat on Thursday deployed oil booms along Port Eads, La., in the Gulf of Mexico. Credit... Sean Gardner/Greenpeace, via Reuters

“Here you have the company that is responsible for the accident leading the response to the crisis,” said Tyson Slocum, director of Public Citizen’s Energy Program. “There is a problem here, and the consequence is clear.”

But it is still the government, in this case the Coast Guard, that has the final say. A law passed a year after the 1989 Exxon Valdez disaster makes "each responsible party for a vessel or a facility from which oil is discharged" liable for cleaning up a spill. But oversight of the cleanup is designated to the Coast Guard, with advice from other federal agencies.