One rather grim data point in the economic recovery from the pandemic: Methane emissions from America’s largest oil field have rebounded. Pollution from the Permian Basin dropped 60% from March to April last year as oil producers shut in wells and cut back on new ones due to tumbling crude prices, according to the non-profit Environmental Defense Fund. But methane emissions are now back at pre-pandemic levels as drilling ramps up, EDF said, citing data from its Permian Methane Analysis Project.

Methane is about 80 times more potent than carbon dioxide over its first two decades in the atmosphere, and President Joe Biden has made eliminating emissions of the gas a priority. But doing so requires regulatory oversight and large investments in pipelines across America’s shale fields, where it’s often cheaper for producers often burn or release gas extracted as a byproduct of more-valuable crude.

Most large producers have pledged to clean up their operations by ending routine flaring, or burning gas, and employ better leak detection methods. Despite this, EDF has found methane emissions to be a persistent problem as it conducts a large-scale study of pollution in the Permian, which stretches across West Texas and southeastern New Mexico.

“Operators in the Permian have historically produced more gas than the region’s facilities – including both upstream and midstream – can manage, straining the system and resulting in the highest emissions observed from any U.S. oil and gas basin,” EDF said in a statement. This “can no longer fly under the policy radar,” said EDF scientist David Lyon.