HOUSTON—Victims of BP PLC’s deadly 2005 refinery explosion have settled all but one of the more than 4,000 lawsuits that were filed in state court after the accident, attorneys and a state district judge said Friday.

Attorneys for blast victims announced Friday that four lawsuits have been settled in the Texas City explosion that killed 15 people and injured more than 170.

State District Judge Susan Criss in Galveston said a hearing is scheduled next month in the only remaining case in state court. There is one lawsuit pending in Houston federal court and attorneys plan to appeal another suit that was dismissed in state court.

The terms of the settlements announced Friday, as has been the case when other blast-related suits have been resolved, were confidential.

“Our clients are very pleased with the settlement, which provide some assurances of security for their long-term financial needs,” said Brent Coon, an attorney for blast victims.

Although various blast-related lawsuits went to trial, all were settled before they reached a jury.

“We are pleased to have resolved substantially all of the claims arising from the March 23 explosion,” London-based BP said in a statement. “Our goal from the outset has been to fairly compensate people harmed by this tragedy. We deeply regret what occurred and are working hard to become an industry leader in the areas of personal and process safety.”

The explosion occurred after a piece of equipment called a blowdown drum overfilled with highly flammable liquid hydrocarbons.

The excess liquid and vapor hydrocarbons were vented from the drum and ignited at the startup of the isomerization unit—a device that boosts the octane in gasoline. Alarms and gauges that were supposed to warn of the overfilled equipment did not work properly.

The U.S. Chemical Safety and Hazard Investigation Board, in its final report, found BP fostered bad management at the plant and that cost-cutting moves by BP were factors in the explosion.

Coon said he is proud of his work to make sure that documents detailing problems at the refinery were made public. Many of these documents were available for viewing on the Web site, www.texascityexplosion.com, which his Beaumont, Texas-based firm started.

He said his firm will continue to focus on improving plant safety, working during next year’s Legislative session to help pass a bill that calls for stronger supervision of petrochemical facilities.

“It was a lot of hard work by a lot of us to get this done,” he said.

Still pending is a decision from a federal judge in Houston on whether she will accept a guilty plea from BP to settle a criminal investigation by the U.S. Department of Justice on the explosion. The much criticized plea deal calls for a $50 million fine and sentences the oil giant to three years’ probation for its role in the blast.

Many blast victims think the fine is low and that BP would not meet its safety obligations at the refinery.

Federal prosecutors and BP have defended the plea agreement, saying it’s the harshest option available in assessing criminal punishment.

A congressional committee is investigating the deal.