And why that's important is a whole host of reasons, but particularly we want to judge the integrity for the use of the blowout preventer on the well either for a capping procedure now or in assistance in the capping procedure with the relief well.

WHITEHOUSE: Press Briefing

As a prelude to permanently shutting down the well, crews are trying to withdraw drill pipe hanging below the bottom of the blowout preventer and remove it from the well, so they can then remove the capping stack that's kept oil from leaking since July 15 and replace the old blowout preventer with a new one.

CNN: STORY HIGHLIGHTS

The next step will be -- and, again, these tests will be important in determining those next steps -- is the decisions to attempt a kill using this blowout preventer or using this blowout preventer simply to assist the relief well drilling, containment and capping procedures.

WHITEHOUSE: Press Briefing

More hazardous still were fires out on oil platforms, such as the Bravo blowout in the North Sea in 1977 and the Piper Alpha disaster, off Aberdeen, in 1988, where the capping of the well had to be done in the face of mountainous seas.

ECONOMIST: Obituary