BP Plc’s record $18.7 billion settlement ended government claims over the 2010 Gulf of Mexico oil spill, leaving numerous smaller private lawsuits to be mopped up.

While investors, residents and businesses that didn’t join a 2012 settlement still demand billions, BP’s biggest threats are gone, said Anthony Sabino, a law professor at St. John’s University in New York who specializes in complex litigation.

The U.S. and the states, partly because of political motivations, “were, by far, the most tenacious adversaries,” he said in an e-mail.

“Private parties think only in terms of cold hard, cash,” so the remaining claims will be easier to resolve, Sabino said. “Put enough on the table and they go away.”

The Macondo well exploded in April 2010, burning and sinking the Deepwater Horizon drilling rig and setting off the biggest offshore spill in U.S. history. Eleven men died aboard the rig and crude spewed from the sea floor for weeks.

The accident sparked thousands of lawsuits against BP, as well as Transocean Ltd., the rig’s owner, and Halliburton Co., which provided cementing services for the project. BP’s predicament got worse as falling oil prices cut first-quarter revenue by 41 percent from a year earlier, to $54.2 billion.

Largest Deal

Thursday’s settlement was the largest of BP’s agreements since the spill. The London-based company agreed in 2012 to plead guilty and pay the government $4 billion to resolve a criminal case. BP also agreed that year to pay another $525 million over allegations it initially understated the size of the spill.

Also in 2012, the company reached an estimated $10.3 billion settlement with most Gulf area residents and businesses harmed by the spill. That deal will probably cost “significantly” more because it doesn’t reflect claims that haven’t been fully processed, the company said in an April regulatory filing.

The settlement didn’t cover banks, casinos, insurance companies and businesses or residents in large swaths of Texas and Florida. It also didn’t include shareholders or businesses blaming BP for the Obama administration’s moratorium on deep- water drilling in the gulf after the spill.

Those claims remain, as do the suits by residents and businesses that opted out of the 2012 settlement.

Spill Cost

On Thursday, BP increased the amount set aside to pay for the spill to $53.8 billion. That still may not be enough.

“It’s realistic to price BP’s total cost, including all remaining claims that haven’t been covered by settlements, at $70 billion,” said David Berg, a Houston trial lawyer who has tracked the BP spill litigation and isn’t involved in it.

None of the claims have gone before a jury, and investors may get the first chance if their securities-fraud lawsuit claiming BP downplayed the disaster goes to trial Jan. 11 in Houston.

The class action covers investors who bought BP’s U.S. shares from April 26, 2010 — six days after the blowout — to May 28, 2010. BP will ask the U.S. Court of Appeals in New Orleans on July 9 to block them from suing as a group, which could derail or delay the case. Investors are seeking as much as $2.5 billion, according to BP court filings.

U.S. District Judge Carl Barbier in New Orleans — who presided over the pollution fine case BP just settled — will oversee a non-jury test trial, still unscheduled, on lawsuits by businesses alleging BP is responsible for losses caused by the drilling moratorium.

Test Trial

One party in the test trial is the successor to Seahawk Drilling and claims the business was “essentially destroyed” and forced into bankruptcy. Seahawk alleges losses of $174.8 million. If the test cases prevail, there could be millions of dollars more in claims from firms including Marathon Oil Co., which seeks $47 million for lost offshore production, and Vantage Drilling Co., which is claiming $265 million for increased financing costs tied to projects delayed by the offshore ban.

BP denies responsibility for those losses because the U.S. government ordered and extended the drilling ban for months. That defense may reduce any damages.

Claims by others left out of the settlement may be a “tough sell to a judge or jury,” Sabino said.

Given Thursday’s settlement as a benchmark,“the dominoes will fall” and the others will probably settle, he said.

The case is In re Oil Spill by the Oil Rig Deepwater Horizon in the Gulf of Mexico on April 20, 2010, MDL-2179, U.S. District Court, Eastern District of Louisiana (New Orleans).

–With assistance from Della Hasselle in Baton Rouge, Louisiana

–With assistance from Della Hasselle in Baton Rouge, Louisiana