CONCORD, N.H. – Nearly a decade after it was first brought, a lawsuit accusing two oil giants of widespread groundwater contamination in New Hampshire is expected to present jurors with the most complex and time-consuming trial in state history.

The products liability case against ExxonMobil and Citgo will be tried beginning in mid-January in a federal courtroom – on loan to the state – because it would undermine the rights of criminal defendants to a speedy trial if it tied up one of the three courtrooms in Merrimack Superior Court, officials said.

The state sued 26 oil companies and subsidiaries in 2003, claiming the gasoline additive MTBE, methyl tertiary butyl ether, caused groundwater contamination in a state where 60 percent of the population relies on private wells for drinking water.