As the Obama administration nears a decision on whether — and how — to clamp down on methane leaking from active oil and gas operations, new research suggests abandoned wells may be a significant source of the potent greenhouse gas.

The study, published Monday in the Proceedings of the National Academy of Sciences, focuses on 19 representative abandoned oil and gas wells in Pennsylvania, it can be extrapolated to the approximately 3 million across the country.

And while federal regulators are now concentrating on methane emitted during oil and gas production, the new study conducted by researchers with Princeton University suggests that accumulating leaks from abandoned wells over decades may be a bigger problem.