Have the benefits of “fracking” as a way to extract natural gas been exaggerated? Australia’s biggest such operation is showing larger than expected leaks of methane, reveals research submitted to a government inquiry.

Burning natural gas, which is mostly methane, creates less carbon dioxide than burning coal. Traditionally accessed deposits are shrinking, so fracturing shale beds to release more gas has become popular. But since methane has a heating effect 25 times greater than that of CO2, accidental leaks could undo the benefits.

Most research on these leaks has focused on well heads, but Damien Maher at Southern Cross University in Queensland and colleagues looked at gas seeping through the ground. They found higher levels of methane in the air above the Tara gas field, suggesting widespread ground leaks. In some places, it hit 6.89 parts per million, over three times the background level. The team suspect fracking changes the soil structure, letting more methane escape. The work is undergoing peer review.

“If it’s leaking from the infrastructure that’s an easy fix,” says co-author Isaac Santos. “If it’s seeping from the soil that’s much harder to fix.”

The Australian Petroleum Production and Exploration Association , which operates the gas field, disputes the findings as “premature”.