A BP executive has told a court that the oil giant and its contractors shared responsibility for preventing blowouts like the one that killed 11 workers in 2010 and sparked America's worst offshore spill.
Lamar McKay, who was president of BP America at the time of the Deepwater Horizon disaster, was the first BP executive to give evidence at a federal trial in New Orleans designed to identify the causes of BP's Macondo well blowout and assign blame to the companies involved.
Rig owner Transocean and cement contractor Halliburton are also defendants at the trial, which started on Monday.
A plaintiffs' lawyer pressed Mr McKay to agree with him that BP bore ultimate responsibility for the blowout, but Mr McKay insisted managing the hazards of deepwater drilling were a "team effort".
"I think that's a shared responsibility, to manage the safety and the risk," said Mr McKay, now chief executive of BP's Upstream unit. "Sometimes contractors manage that risk. Sometimes we do. Most of the time it's a team effort."
Mr McKay said the rig explosion and spill in the Gulf of Mexico was a "tragic accident" resulting from a "risk that was identified".
His evidence followed that of an expert witness for people and businesses suing the company.
University of California-Berkeley engineering professor Robert Bea said BP did not implement a two-year-old safety management programme on the rig that exploded in the Gulf of Mexico on April 20, 2010.
"It's a classic failure of management and leadership in BP," said Prof 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, Prof Bea said the company made "significant efforts" to improve safety management as early as 2003. But BP 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.