The results suggest that leaks of methane could be a problem for drilling across the nation, said study lead author Cornell University engineering professor Anthony Ingraffea, who heads an environmental activist group that helped pay for the study.
The research was criticized by the energy industry. Marcellus Shale Coalition spokesman Travis Windle said it reflects Ingraffea's "clear pattern of playing fast and loose with the facts."
The Marcellus shale formation of plentiful but previously hard-to-extract trapped natural gas stretches over Pennsylvania, West Virginia and New York.
The study was published Monday by the Proceedings of the National Academy of Sciences.
A team of four scientists analyzed more than 75,000 state inspections of gas wells done in Pennsylvania since 2000.