Two energy trade groups in the United States said their study of natural gas production found emissions levels at half of what the EPA reported. The American Petroleum Institute and America\'s Natural Gas Alliance said methane emissions from the processes tied to shale natural gas production were lower than what the Environmental Protection reported in an April survey. Howard Feldman, director of regulatory and scientific affairs at API, said the joint study was based on emissions from more than 91,000 wells, compared with 8,800 wells surveyed by the EPA. \"Our new report provides the best, most comprehensive estimate of methane emissions from U.S. natural gas production,\" he said in a statement. Specifically, the API/ANGA study said methane emissions from liquids unloading, the process used to remove water from wells to improve natural gas flow, was 86 percent lower than the EPA estimated. Refracturing, a technique meant to prolong production life of existing wells, reportedly produced 72 percent fewer emissions than the EPA figures. Combined, the API and the ANGA represent the interests of more than 500 oil and natural gas companies. Sierra Club attorney Craig Segall said that despite the discrepancy in figures, natural gas production was still a significant source of greenhouse gas emissions, The Oklahoman newspaper reports.