HARRISBURG — Pennsylvania on Thursday sued a long list of oil companies over the groundwater pollution caused by leaks and spills of gasoline containing the additive MTBE, and also alleged that companies improperly accepted financial help from a state-run fund to clean up many other spills.

The offices of Gov. Tom Corbett and Attorney General Kathleen Kane said the two separate lawsuits were filed Thursday in Philadelphia city courts.

The about 50 defendants named in the MTBE lawsuit include MTBE manufacturers, gasoline refiners, marketers and distributors that together controlled virtually the entire MTBE market in Pennsylvania, the lawsuit said.

Pennsylvania is seeking to recover millions of state dollars spent to clean up and monitor MTBE, as well as damages and penalties for marketing MTBE. The oil companies knew, or should have known, it was a potent threat to groundwater, the suit said.

The state has spent more than $738 million to investigate and clean up about 3,400 gasoline spills or leaks since 1994, a substantial portion of which have involved MTBE, the suit said.

The companies’ conduct was “wanton, malicious, oppressive and fraudulent,” the lawsuit said, and they “fraudulently, deceptively and unfairly” marketed MTBE as safe for the environment.

“The injuries and threatened injuries from MTBE contamination are statewide and involve and affect in a substantial way a significant portion of the state’s population,” the lawsuit said.

It has been detected in groundwater throughout the state, the lawsuit said, and is a known carcinogen. The U.S. Environmental Protection Agency calls MTBE a “potential human carcinogen at high doses.”

The chemical was added to gasoline to reduce smog, but was found to be more soluble than gasoline and traveled farther and faster in groundwater.

The lawsuit comes in the wake of a U.S. Supreme Court decision in April not to overturn a $105 million verdict against Dallas-based Exxon Mobil Corp. for contaminating New York City’s groundwater. Vermont filed a similar MTBE lawsuit earlier this month and New Hampshire last year won a $236 million verdict against Exxon Mobil.

A spokesman for Exxon Mobil, which was named as a defendant by Pennsylvania in the MTBE lawsuit, said company officials had not yet reviewed it. But, in an e-mail, spokesman Todd Spitler said energy companies that complied with the law to blend oxygenates in gasoline should not later be held liable.