The trial over the 2005 accident, which killed 15 people and injured 170, began on September 5. It was the only one of hundreds of lawsuits stemming from the blast to reach the courtroom.
"It occurred overnight," BP spokesman Neil Chapman said after the deal was announced in court. "We don't talk about the settlements. All I can say is we've worked since the explosion to settle so people don't have to go to court."
BP declined to provide details on the suit. More than 1,300 other suits have been settled. Before the latest settlement, the explosion cost the London oil company at least $US2 billion ($A2.4 billion) in compensation payouts, repairs and lost profit.
The explosion at the plant, located about 65km south-east of Houston, occurred after a piece of equipment called a blowdown drum overfilled with highly flammable liquid hydrocarbons.
The excess liquid and vapour hydrocarbons were then vented from the drum and ignited as the isomerisation unit - a device that boosts the octane in petrol - started up. Alarms and gauges that were supposed to warn of the overfilled equipment didn't work properly.
The US Chemical Safety and Hazard Investigation Board, one of several agencies that probed the accident, found BP fostered bad management at the plant and that cost-cutting moves by BP were factors in the explosion.
BP released an internal report in May that said the plant's culture seemed to ignore risk, tolerate noncompliance and accept incompetence.
The brief trial featured testimony from Don Parus, the plant's former manager, who defended the company's safety record and denied assertions that profits drove delays in repairs.
Brent Coon, a lawyer for the four workers who attributed their injuries to the blast, tried to contrast Parus' comments with a study two months before the blast in which workers told of various safety problems at the plant.
At one point Parus was asked by Coon if he agreed with a description of the isomerisation unit as "a piece of junk" that should have been repaired. When Parus refused to describe the unit this way, Coon tried to compare him to an ostrich, asking him if he had his head stuck in the sand the last two-and-a-half years.
Parus, who is on paid administrative leave, said he was surprised by many employee comments in the report, which he had requested. But he said many of the comments in the report were workers' opinions of what they saw at the refinery.
Parus also told jurors that before the accident, BP did not recognise the risk of placing trailers around the isomerisation unit. All 15 deaths in the accident happened in the two trailers closest to the blast site. Since the explosion, BP has removed all temporary structures from the refinery.
A fifth lawsuit that was also set to be tried, filed by the estate of a contract worker whose suicide was attributed to trauma from the accident, was settled just before the trial began.
