CONCORD, N.H. -- Exxon Mobil Corp. was found liable Tuesday in a long-running lawsuit over groundwater contamination caused by the gasoline additive MTBE, and the jury ordered the oil giant to pay $236 million to New Hampshire to clean it up.

The jurors reached their verdicts in less than 90 minutes, after sitting through nearly three months of testimony. Lawyers on both sides were stunned by the speed with which they reached the verdict on liability and even more stunned when the jurors took barely 20 minutes more to fill out the damages verdict.

Juror Dawn Booker of Pembroke told The Associated Press that all 12 felt "very, very confident about our decision."

The panel awarded the state all $236 million it was seeking from Exxon Mobil to monitor and remediate groundwater contaminated by MTBE. The chemical was added to gasoline to reduce smog but was found to travel farther and faster in groundwater than gasoline without the additive.

Attorney General Michael Delaney said he anticipates an appeal and doesn't expect to see the money "anytime soon." He said the case and the verdict are historic.

The verdict is more than twice the $105 million jurors awarded the New York City Water District in 2009 in its case against Exxon Mobil over MTBE contamination. That case is on appeal.

Jessica Grant, the state's lead lawyer, said it was the largest verdict ever in an MTBE case, though a financial analyst noted that the award represents about two days' worth of profit for the company.

Jurors found that Exxon Mobil was negligent in adding MTBE to its gasoline and that it was a defective product. They also found Exxon Mobil liable for failing to warn distributors and consumers about its contaminating characteristics.

Jurors also rejected Exxon Mobil's defense that more than 300 junkyard and gas station owners not named in the lawsuit were responsible for much of the contamination. They also absolved the state of responsibility for the contamination.

The jury found damages in the amount of $816 million, but that award was reduced to 28.9 percent of the total -- reflecting Exxon's market share of gasoline sold in the state between 1988 and 2005.

The U.S. Environmental Protection Agency has classified MTBE as a "possible human carcinogen." New Hampshire banned its use in 2007.

The state says more than 600 wells in New Hampshire are known to be contaminated with MTBE and an expert witness estimated the number could exceed 5,000.