McKay's testimony, meanwhile, wasn't his first under oath. In May 2010, he went before Congress only weeks after the disaster and said BP's Operating Management System is "as good as anyone."
BP has already pleaded guilty to manslaughter and other criminal charges and has racked up more than $24 billion in spill-related expenses, including cleanup costs, compensation for businesses and individuals, and $4 billion in criminal penalties.
Plaintiffs' attorney Robert Cunningham read portions of the plea agreement as he pressed McKay to say how much responsibility BP takes for the catastrophe. Cunningham noted that nothing in the document assigns blame to specific BP executives.
"That is not written in there. That's true," McKay said.
Two BP rig supervisors, however, have been indicted on manslaughter charges for the workers' deaths and are awaiting a separate trial.
"There were some misinterpretations and mistakes made" on the rig, McKay said.