CONCORD, N.H. (AP) - The state of New Hampshire is launching its case against two major oil companies in what is expected to be the longest and most complex trial in state history. The state's lawyers say ExxonMobil and Citgo should pay more than $700 million in damages to monitor and clean up groundwater contamination caused by the gas additive MTBE - methyl tertiary butyl ether - now banned in New Hampshire. Lawyers for the oil companies say they have cleaned up their own sites and that contamination elsewhere was caused by third parties not named in the suit. The lawsuit - filed in 2003 - is the only one brought by a state to reach trial on the issue of MTBE groundwater contamination. Most of the other MTBE cases nationwide were brought by municipalities, water districts or individual well owners, and all but one was settled or dismissed. The jury trial begins Monday and is expected to last four months. It is being held in a federal courtroom on loan to the state so as not to monopolize one of three courtrooms at Merrimack Superior Court. More than 50,000 exhibits have been marked and the witness list numbers 230. It was clear from a pretrial conference Friday that jurors will be confronted with an alphabet soup of acronyms for various funds and agencies, will have to grapple with complex statistical analyses and will hear contradictory testimony by expert witnesses. MTBE had been used in gasoline since the 1970s to increase octane and reduce smog-causing emissions. While it was credited with cutting air pollution, it was found in the late 1990s to contaminate drinking water when gasoline is spilled or leaks into surface or groundwater. New Hampshire banned its use in 2007. Roughly 60 percent of New Hampshire's population gets its drinking water from wells, which drives up the estimated cost to test and treat contaminated water sources.