About 11 hours before the Deepwater Horizon exploded, a disagreement took place between the top manager for oil giant BP PLC on the drilling rig and his counterpart for the rig's owner, Transocean Ltd. , concerning the final steps in shutting down the nearly completed well, according to a worker's sworn statement.

Michael Williams, a Transocean employee who was chief electronics technician on the rig, said there was "confusion" between those high-ranking officials in an 11 a.m. meeting on the day of the rig blast, according to a sworn statement from Mr. Williams reviewed by The Wall Street Journal. Mr. Williams himself attended the meeting.

The confusion over the drilling plan in the final hours leading up to the explosion could be key to understanding the causes of the blowout and ultimately who was responsible.

What is known from drilling records and congressional testimony is that after the morning meeting, the crew began preparations to remove from the drill pipe heavy drilling "mud" that provides pressure to keep down any gas, and to replace this mud with lighter seawater.

Ultimately, the crew removed the mud before setting a final 300-foot cement plug that is typically poured as a last safeguard to prevent combustible gas from rising to the surface. Indeed, they never got the opportunity to set the plug.