NEW ORLEANS, Louisiana (AFP) - Prosecutors accused BP of letting greed triumph over safety on Monday in the opening of a multi-billion dollar trial over the devastating 2010 Gulf of Mexico oil spill.

A federal judge in New Orleans is tasked with determining how much BP and its subcontractors should pay for the worst environmental disaster in US history.

US prosecutors are determined to prove that gross negligence caused the April 20, 2010 blast that killed 11 workers and sank the BP-leased Deepwater Horizon rig, sending millions of barrels of oil gushing into the sea.

The US government plans to introduce ample evidence of "systemic problems of corporate recklessness" and how a "culture of disregard to safety" led to the blowout, said Mr Michael Underhill, lead trial counsel for the United States. "Reckless actions were tolerated, sometimes encouraged by BP to squeeze every dollar," he told the court.

"Every fork in the road, BP chose time and money over safety in the operation of what (one rig worker) called the 'well from hell.'"

BP is equally determined to avoid a finding of gross negligence, which would drastically increase its environmental fines to as much as US$17 billion (S$21 billion).

BP is also hoping to shift much of the blame - and cost - to rig operator Transocean and subcontractor Halliburton, which was responsible for the runaway well's faulty cement job.

Transocean's poor safety record was the focus of the first lawyer to speak, Jim Roy, who represents thousands of individuals and businesses impacted by the spill through a steering committee.

Mr Roy told the court that the Swiss giant's top safety official on the multimillion dollar rig "was not even minimally competent for this job." "His training consisted of a three-day course. Amazingly, he had never been aboard the Deepwater Horizon," Mr Roy said, noting that the blowout was the seventh major incident aboard a Transocean rig in the space of 17 months.

Transocean defended its "well-trained" crew whose "death-defying acts of heroism" ensured that "every single man and woman who could have survived, did," and described BP's attempt to shift the blame as "shameful." "None of this had to happen. It happened because BP was behind schedule and needed to get this done," said Mr Brad Brian, Transocean's lead attorney.

"BP considered another alternative to this: Plug the well and abandon it. but that would have cost over US$10 million." Louisiana Attorney General Buddy Caldwell urged the judge to ensure that BP and its contractors bear responsibility for their actions.

"Today, less than 30 miles from the door of this courthouse, over 212 miles of Louisiana coast are being polluted and continue to be oiled," he told the court.

It took 87 days to cap BP's runaway well, which blackened beaches in five states and crippled the region's tourism and fishing industries in a tragedy that riveted the nation.

The British energy giant has already resolved thousands of lawsuits linked to the deadly disaster out of court, including a record US$4.5 billion plea deal with the US government in which BP pleaded guilty to criminal charges and a US$7.8 billion settlement with people and businesses affected by the spill.

BP spent more than US$14 billion on the response and cleanup and paid another US$10 billion to businesses, individuals and local governments that did not join the class action lawsuit.

It remains on the hook for billions in additional damages, including the cost of environmental rehabilitation.

The first phase of the civil trial will determine the cause and apportion fault for the disaster.

The second phase, not expected to start for several months, will determine exactly how much oil was spilled in order to calculate environmental fines.

The third phase will deal with environmental and economic damages.

Protesters camped outside the courthouse said they hope that Judge Carl Barbier will assess the maximum penalties possible under the law.

"This is not just about something that's going to take decades to clean up," said Chris Canfield, vice president of Gulf of Mexico conservation and restoration for the National Audubon Society.

"This is about making sure that bad actors are punished for a series of decisions that put profits ahead of people and the environment."