Petroleum and natural gas systems in the United States accounted for 40 percent of the methane emissions reported to U.S. EPA in 2011, the first year that emissions from oil and gas were included in the agency's greenhouse gas inventory. That translates to 83 million metric tons carbon dioxide equivalent (CO2e) of methane, a potent greenhouse gas, reported to EPA. Including carbon dioxide and other greenhouse gases, the industry emitted 225 million metric tons of CO2e.