"I think that's a shared responsibility, to manage the safety and the risk," said McKay. "Sometimes contractors manage that risk. Sometimes we do. Most of the time it's a team effort."
McKay also defended BP's internal probe of the spill, which outlined a series of mistakes by rig workers and faulted decisions by other companies but didn't assign any blame to BP's upper-level management.
"I think it was a substantial investigation," McKay said. "I think we've learned what we can from the accident and we're trying to put those things into practice right now."
One of the biggest issues already emerging early at trial is BP's safety record.
University of California-Berkeley engineering professor Robert Bea testified earlier Tuesday that BP PLC didn't implement a 2-year-old safety management program on the rig that exploded.
"It's a classic failure of management and leadership in BP," said Bea, a former BP consultant who also investigated the 1989 Exxon Valdez spill and New Orleans levee breaches after Hurricane Katrina in 2005.
BP has said its "Operating Management System" was designed to drive a rigorous and systematic approach to safety and risk management. During cross-examination by a BP lawyer, Bea said the company made "significant efforts" to improve safety management as early as 2003.
However, the plaintiffs say BP only implemented its new safety plan at just one of the seven rigs the company owned or leased in the Gulf at the time of the disaster.
BP lawyer Mike Brock said the company allows contractors like Transocean to take the primary responsibility for the safety of rig operations as long as the contractor's safety system is compatible with BP's — an arrangement Brock suggested is a standard industry practice.