But Angie Burckhalter, speaking on behalf of the Oklahoma Independent Petroleum Association and the Independent Petroleum Association of America, also elicited enthusastic clapping after describing fracking as "a safe, proven technology that has been used over one million times for 60 years."

Fracturing is vital to producing "clean energy that makes modern life possible," she said.

Texas Railroad Commission Chairman Victor Carrillo also strongly defended fracturing, saying that without it, gas recovery from tight rock formations such as the Barnett Shale -- the leading gas-producing area in the nation -- would be "impossible." There are no documented cases of fracturing causing groundwater contamination in Texas, he said, drawing both cheers and boos.

Meeting moderator Adam Saslow repeatedly implored audience members to tone down, urging them to employ "manners your mother taught you."

Calvin Tillman, an outspoken critic of the oil and gas industry and mayor of the Denton County community of Dish, held up a container of murky water and said it came from the home of a resident who fears his water well has been contaminated by Barnett Shale operations.

In considering stronger regulation, the foremost concern should not be about what might "negatively affect Chesapeake or Devon," Tillman said, referring to two large gas producers. Instead, the emphasis should be on negative effects on drinking water, he said.

America's Natural Gas Alliance, which represents 34 independent gas exploration and production companies, defended fracking and pledged to "be a constructive participant in the progress of the [EPA] study going forward."

"We are confident that a scientifically sound and data-driven examination will provide policymakers and the public with even greater reassurance of the safety of the longstanding practice," ANGA said in a statement.