After nearly two years measuring methane emissions from more than 100 natural gas hydraulic fracturing sites across the country, researchers at the University of Texas at Austin and several other institutions published their findings on Monday. While the total amount of methane emissions they found was similar to older federal estimates, key differences in the amount of emissions linked to certain drilling practices and equipment could have broader implications for federal regulatory policy and oil and gas companies' own activities.

The findings are meaningful because the study is one of the most comprehensive looks yet at the amount of methane emissions that come from the production of natural gas, which is seen as a clean energy source that can combat climate change. Previous studies have produced conflicting results; this study, unlike previous ones, measured emissions right at the source. Methane emissions are one of the leading contributors to climate change, and environmentalists fear they will counteract the benefits of using natural gas.

The results are sure to be controversial. Just minutes after the study was released, some environmental and accountability groups were already questioning the validity of the data, since 90 percent of the $2.3 million in funding for the research came from nine participating oil and gas companies.

Wenonah Hauter, executive director of the Washington, D.C.-based Food and Water Watch, called the study "more spin than science." And the research nonprofit Public Accountability Initiative alleges that one of the study's authors, Jennifer Miskimins, failed to disclose her employment with a petroleum engineering firm in Colorado. She is listed in the study as a member of the Department of Petroleum Engineering at the Colorado School of Mines. Miskimins did not respond to a request for comment.

Researchers said company funding and participation was critical so they could get access to well sites and collect data, but added that the industry did not have any say in how the data would be interpreted.

Allegations of bias, old data and changing technology have long raised questions about how much the natural gas production and supply chain contributes to methane emissions. “There’s been a lot of debate,” said David Allen, a UT-Austin chemical engineering professor and the main author of the study.

The researchers found that the amount of methane emissions being released by natural gas drilling and production was similar to what the federal Environmental Protection Agency had estimated in the past. But there were key differences that could have an impact on regulatory policy going forward.

In response to what Allen called "uncertainty in the scientific literature” on the methane emissions that come from “well completions” — when a newly drilled gas well is cleaned of sand and other liquids used to release gas from underground rock formations — the researchers measured methane emissions at 27 well completions across the country. (The EPA has required the industry to use equipment that will limit such emissions on all new wells by 2015.)

The researchers found those emissions were far lower than what the EPA had estimated, even for those wells that were not yet using the new equipment. But they found that emissions from other pieces of equipment on the well sites, such as certain chemical injection pumps, were much higher than previous EPA estimates.

“The implication is that we need to think about ways to find leaks and repair them,” said Ramon Alvarez, senior scientist at the Environmental Defense Fund’s Texas office. Now that regulations are in place to address well completion emissions, he said, “I think that’s the direction the conversation will take over time.” EDF provided about 10 percent of the funding for the study.

Some key methane emission questions remain unanswered. The Environmental Defense Fund is funding other research projects that would measure them at other points in the natural gas supply chain, including processing, transmission and local distribution.

Another limitation of the methane study is that it focuses only on the impacts of hydraulic fracturing for natural gas. But a dive in natural gas prices has resulted in far more drilling for oil in recent years. According to the state's Railroad Commission, which regulates oil and gas drilling, energy companies completed nearly 11,000 oil wells in Texas in 2012. They only completed about 3,500 gas wells in the same year. And some areas they first drilled for gas are now being mined for oil instead, but there is much less data available on emissions from those activities.

“It used to be, they went for the gas, and now they’re going for the oil,” Alvarez said, adding that researchers are beginning to look more closely at emissions from oil drilling. “Hey, you know, these oil wells have emissions, too. You have an opportunity to control them.”