Environmentalists are fighting with energy firms over current pollution laws from which the oil industry is exempt. Currently there is little or no federal oversight over a drilling process used to extract natural gas. The process involves injecting water, mixed with sand and chemicals, to crack rock deep below the Earth's surface and release the gas trapped within it.

"Oil and gas companies can pump hundreds of thousands of gallons of fluid—containing any number of toxic chemicals—into sources of drinking water with little or no accountability," said Rep. Henry Waxman, chair of the House Committee on Oversight and Government Reform.

But Lee Fuller, vice president of government relations for the Independent Petroleum Association of America says the industry drills well below any aquifers that may supply drinking water and uses extra safety guards when doing it.

Oil and gas companies involved in exploration and production also are exempt from reporting emissions to the Toxic Release Inventory, a public database maintained by the Environmental Protection Agency. Nationwide, the number of gas-producing wells increased to 425,000 from 270,000 from 1990 to 2005, according to the U.S. Energy Information Administration. And in 2006, oil and gas companies drilled nearly 30,000 more gas wells and 15,000 new oil wells, according to the American Petroleum Institute.