Oil and natural gas systems represented the second largest source of greenhouse gas (GHG) emissions in the United States last year, but methane emissions actually fell 1% because of an increase in natural gas drilling, according to the U.S. Environmental Protection Agency (EPA).

The Greenhouse Gas Reporting Program data, issued on Tuesday by the EPA, details GHG pollution trends and emissions broken down by industrial sector, geographic region and individual facilities.

In 2013, reported emissions from large industrial facilities were 20 million metric tons, or 0.6%, higher than in 2012, mostly because of an increase in coal use for power generation, according to federal statistics. More than 8,000 large emitters reported direct GHG emissions to the program for 2013, representing almost half of total domestic sources.

Power plants were the largest source of domestic emissions in 2013, with more than 1,550 facilities emitting 2 billion metric tons-plus of carbon dioxide, roughly 32% of total U.S. GHG pollution. Emissions from power plants have declined by 9.8% since 2010, but there was an uptick in emissions of 13 million metric tons in 2013 because of increased coal use.

The second largest stationary source, petroleum and natural gas systems, reported 224 million metric tons of GHG emissions, which was a 1% decrease from 2012.

“Reported methane emissions from petroleum and natural gas systems sector have decreased by 12% since 2011, with the largest reductions coming from hydraulically fractured natural gas wells, which have decreased by 73% during that period. EPA expects to see further emission reductions as the agency’s 2012 standards for the oil and gas industry become fully implemented,” federal officials said.

Refineries were the third largest stationary source, reporting 177 million metric tons of greenhouse gas emissions, up 1.6% from the previous year. Reported emissions from other large sources in the industrial and waste sectors increased by 7 million metric tons of greenhouse gas pollution, up 1% from 2012.