Penning said politics in his state have hampered efforts to put together a systematic study of the risks involved in fracking. "In Pennsylvania, we've had a very pro-drilling legislature since Tom Corbett became governor," he said.

"industry...needs to learn by practice"

Proponents of industry-funded research say that in most cases the system works.

At Harvard University's Belfer Center for Science and International Affairs, 12 members of the "international council" have ties to the oil and gas industry, including three directors. The Public Accountability Initiative argues that those ties raise questions about potential pro-industry bias in the center's research.

Sharon Wilke, a representative for Harvard's Belfer Center, said that the University and Center "take a number of steps to ensure the integrity of its scholarship." That includes, she said, a requirement that all grant and gift agreements protect faculty members' "rights to publish their findings and conclusions where and how they see fit, free of undue sponsor or donor influence."

Engelder, of Penn State, said that critics of continued fracking miss a simple reality: To fully understand the risks and rewards of fracking, you have to actually do it.

"This is a very complex industry that needs to learn by practice," he said. "In New York State, for example, the moratorium has been put on by people who say we need to study this more. When you look at what that really means, it means let's look at what's happened in Pennsylvania."

"I don't think the industry has moved too rapidly, because the industry really needed the experience to come across the problems that then needed to be expected," Engelder added. "And it is my contention that the industry has learned from its mistakes and has fixed them. My point is you find the leaks and you fix them. And I think the engineering is there to do that."