US government prosecutors, on the first day of trial related to the fatal 2010 Gulf of Mexico oil spill, have accused that BP and Transocean officials’ negligence of an oil-rig safety test was one of the main reasons behind the explosion, which killed 11 people.

US Justice Department lawyer Michael Underhill and attorney for plaintiffs Jim Roy, who sued the companies, noted that BP and Transocean supervisors failed to accurately interpret the results of a pressure test on the Macondo well off the coast of Louisiana, which resulted in the devastating accident.

The blowout and explosion on the Deepwater Horizon drilling rig spewed four million barrels of oil into the Gulf waters, one of the largest oil spills in US history, reported Bloomberg News.

Underhill was quoted by the news agency in opening statements as saying, "BP put profits before people, profits before safety and profits before the environment."

Underhill also argued that BP executives’ "missteps and reckless decisions" about the safety test were provoked by pressure to generate billions in profits regardless of the costs.

The lawyer said that BP executives could have evaded the explosion if an on-site supervisor walked over the drilling area and stopped operations after issues were raised about the negative-pressure test.

If BP, the well’s owner, is found guilty of gross negligence, it will have to pay the US up to $17.6bn as Clean Water Act fines.

BP will also be liable to unspecified punitive damages to claimants, who were not part of the $8.5bn settlement, which the company reached in 2012.

If gross negligence is found against Transocean and Halliburton, it would mean the companies would be held liable for punitive damages.