Trucks used in the fracking industry sit at a truck stop in Odessa, Texas, on February 4.
Pumpjacks and wells churn away at an oil field on the Monterey shale formation in March 2014. Opponents of fracking in California cite increased water usage amid a devastating drought and possible chemical pollution as primary reasons for denouncing the operations. There are also concerns about fracking disturbing the already volatile, 800-mile-long San Andreas Fault.
Steve Lipsky of Parker County, Texas, near Dallas, holds photographs of his well water burning during a briefing organized by anti-fracking groups in Washington in February 2014.
A fracking facility and its working wells serve as a backdrop to field workers picking potatoes in Shafter, California, in June 2013.
A pumpjack drills for oil at the Monterey shale formation in California in April 2013. The U.S. government estimates that as many as 15 billion barrels of oil could lie within the formation, but most of it is not retrievable without fracking.
Steve Lipsky lights water flowing from a well spigot on his family's property in Parker County, Texas, near Weatherford, in November 2012. Lipsky says a fracking operation contaminated the well.
A worker monitors water pumping pressure and temperature at an Encana Oil & Gas fracking site in Rifle, Colorado, in March 2013.
Signs protesting the process of fracking are posted near Callicoon Center, New York, in January 2012. Although oil companies hail fracking as an innovative way to boost gas reserves, the process has drawn a fair number of detractors.
Gas flares at a water facility at the Niobrara oil shale formation in Colorado in May 2012.
A gas pipeline protrudes from the ground at a farm outside Dimock, Pennsylvania, in March 2012. Proponents of fracking say petroleum extraction is good for the economy and boosts national security by providing more energy sources.
Rig workers drill a saltwater well to get fluids to be used in a fracking operation in Anthony, Kansas, in February 2012.
A worker marks pipes being used at Chesapeake Energy's fracking site in Carroll County, Ohio, in October 2011.
Traffic generated by an oil boom lines the main street in Watford City, North Dakota, on October, 11, 2011. The Bakken oil formation, which stretches from South Dakota into Saskatchewan and could contain more than 4 billion barrels of oil, has sparked an oil boom in towns like Watford City.
A crew constructs a 10-inch gas pipeline outside Watford City, North Dakota in October 2011. In fracking, water, sand and chemicals are injected under high pressure into a gas well.
A Halliburton employee monitors a fracking operation outside Hope, New Mexico, in June 2007. Fracking, or hydraulic fracturing, is the process of breaking through dense shale to unlock natural gas.