Methane continues to escape at a high rate from oil and gas operations in the Permian Basin, according to an aerial survey released Dec. 14 that detected major methane plumes from 40% of 900 sites that were measured.

The latest research conducted by the Environmental Defense Fund (EDF) via helicopter during the first two weeks of November found that 14% of those plumes were the result of malfunctioning flares.

Researchers also found that at one-third of smaller wells significant emissions persisted for days. The aerial survey of the largest U.S. oil field showed that leaks arose from different pieces of equipment at different times.

This was the eighth aerial survey conducted by EDF’s PermianMAP initiative, which monitors methane from the upstream, downstream and midstream operations in the oil field. The survey comes weeks after the U.S. EPA proposed the first regulations targeting methane from the country’s existing oil and gas facilities.

The Biden administration also set a goal to reduce 30% of all methane emissions by 2030 as part of its participation in the Global Methane Pledge, which was formally launched at the U.N. Climate summit in Glasgow.

“This research makes clear that the agency [EPA] must tackle frequent, large emissions from smaller wells if we’re going to have a shot at achieving our climate goals and protecting communities from air pollution,” said Jon Goldstein, senior director of regulatory and legislative affairs at the EDF.

Oil and gas companies that operate in the Permian Basin have tried to show they intend to address the high rate of methane emissions from the basin ahead of the forthcoming EPA rules.

The Permian Basin accounts for 20% of Exxon Mobil Corp.’s total oil and gas operations. The oil major said on Dec. 13 it will deploy advanced satellite technology and data-processing platforms to detect methane emissions.