DENVER — A new report from the Center for American Progress has identified the top 11 companies responsible for nearly half of all methane pollution in the United States.

Methane is 87 times more potent than carbon dioxide at trapping heat in the atmosphere. Sara Loflin, executive director of the League of Oil and Gas Impacted Coloradans, said the state has made progress reducing emissions, but more needs to be done.

“Colorado is really a pioneer and has done a really good job of leading the way in trying to get oil and gas companies to clean up their act and to start to reduce the amount of methane that they’re releasing,” she said. “It’s really a regional problem as well, that we need to start to look at.”

Last month, the Environmental Protection Agency set limits on methane pollution from new oil and gas sites, but according to the report, by 2018 nearly 90 percent of all emissions will come from existing wells and equipment. It makes the case that those sites need stronger standards as well. The oil and gas industry has said the new rules are unnecessary because it already has reduced emissions on its own.

The study found that Colorado’s Anadarko and San Juan basins are among regions with the highest pollution levels in the country. For communities in Garfield and Mesa counties — areas that routinely get failing air-quality grades from the American Lung Association — limiting methane emissions is a public health issue, Loftin said.

“It is absolutely time that we start to really address the air-quality issue in the state,” she said, “not just for environmental reasons but also for day-to-day health of Colorado residents.”

Companies operating in Colorado that made the “who’s who” list of top methane polluters include ConnocoPhillips, ExxonMobil and Anadarko Petroleum.