BP PLC may have reached a provisional settlement with private plaintiffs suing the oil giant over the Deepwater Horizon disaster, but now it faces an even bigger challenge: making a deal with the federal government.

The company announced Friday night that it has reached a provisional $7.8 billion settlement with a group of attorneys representing private plaintiffs who sued in the aftermath of the April 20, 2010, explosion and subsequent leak in the Gulf of Mexico.

The money will be paid from the $20 billion trust BP had already set up to compensate Gulf state residents via the Gulf Coast Claims Facility administered by attorney Kenneth Feinberg.

The deal struck Friday -- which covers claims from individuals and businesses -- meant that a trial on BP and its partners' liability for the disaster, which was due to commence today in New Orleans, has been postponed indefinitely.

The settlement with the plaintiffs, which still has to be finalized and signed off on by U.S. District Judge Carl Barbier of the Eastern District of Louisiana, does not mean the trial won't ever happen. Many legal issues still remain unresolved.

Crucially, the deal does not include any government entities, including the federal government. The Justice Department has a major civil enforcement action pending against BP and partners Transocean Ltd. and Anadarko Petroleum Corp. Last month the government settled claims against MOEX Offshore 2007 Ltd., which had a minor stake in the well, for $90 million.

As Rob Verchick, a law professor at Loyola University, New Orleans College of Law, described it in a blog post today, if the litigation is viewed in culinary terms, the settlement with the plaintiffs is merely an appetizer.

"The main course -- a pepper pot of federal civil claims and criminal charges -- has yet to come," Verchick said. "And that's a dish that could really bust a gut."

The government is seeking penalties for violations of the Clean Water Act and the Oil Pollution Act. Under the Clean Water Act alone, BP faces penalties of $1,100 per barrel spilled. That amount could rise to $4,300 a barrel if the government could prove that the company was grossly negligent.

As an estimated 4.9 million barrels of oil were spilled, a potential settlement could therefore be in the billions of dollars. The terms would be likely to include requirements that BP undertake various environmental projects in the Gulf (Greenwire, Feb. 23). Under the natural resources damage provisions of the Oil Pollution Act, BP is also required to pay for environmental restoration.

John Cruden, a former senior Justice Department official who is now president of the Environmental Law Institute, said the settlement with the plaintiffs "should not affect the legal claims being pressed by the federal government, Gulf states and local governments."

It is also significant that no criminal charges have been filed yet, he added. The threat of a criminal prosecution gives the Justice Department extra leverage during negotiations, lawyers familiar with such talks say.

Cruden said the only real impact of the settlement with the plaintiffs is that it "will allow more focused discussions with the government" in the months ahead.

James Rubin, another DOJ veteran, said what the settlement did show is that "BP is seeking to resolve its alleged liability without costly and prolonged litigation."

But he noted that the settlement with the plaintiffs "may have been easier to swallow" because BP had already allocated the funds to the Gulf Coast Claims Facility.

"The fact that they haven't settled with the U.S. yet may indicate BP is facing tougher demands from the U.S. in terms of penalties and other requirements," said Rubin, who is now in private practice with SNR Denton.

In response to questions, DOJ issued a statement saying that officials are "open to a fair and just settlement" but are also "fully prepared to try the case."

The department is continuing "to work closely with all five Gulf states to ensure that any resolution of the federal law enforcement and damage claims, including natural resources damages, arising out of this unprecedented environmental disaster is just, fair and restores the Gulf for the benefit of the people of the Gulf states," the statement said.

BP declined to comment on the status of any negotiations with the Justice Department. The company's share price was up by 1.5 percent on the first day of trading since the settlement was announced.