Workers use perforating tools to create fractures in rock. An EPA study finds that "fracking" to reach and extract deep pockets of hydrocarbons has not caused widespread drinking water pollution. Brennan Linsley/AP hide caption

itoggle caption Brennan Linsley/AP

Austin Holland, research seismologist at the Oklahoma Geological Survey, gestures to a chart of Oklahoma earthquakes in June 2014 as he talks about recent earthquake activity at his offices at the University of Oklahoma in Norman, Okla. The state had three times as many earthquakes as California last year. Sue Ogrocki/AP hide caption

itoggle caption Sue Ogrocki/AP

Interior Secretary Sally Jewell speaks in Anchorage, Alaska. The Obama administration is requiring companies that drill for oil and natural gas on federal lands to disclose chemicals used in hydraulic fracturing operations. Dan Joling/AP hide caption

itoggle caption Dan Joling/AP

A platform owned by Mexico's state-run oil company Pemex is seen off the Bay of Campeche in the Gulf of Mexico. The country has recently opened up its energy sector to foreign investors. Victor Ruiz/Reuters/Landov hide caption

itoggle caption Victor Ruiz/Reuters/Landov

Opponents of fracking protested in January at the inauguration of Pennsylvania Gov. Tom Wolf. Matt Rourke/AP hide caption

itoggle caption Matt Rourke/AP

A functioning oil rig sits in front of the capital building in Oklahoma City, Okla. The oil industry is an important employer in the state, but officials are concerned a technique used to dispose of wastewater from oil extraction is behind a surge in earthquakes here. Frank Morris/KCUR hide caption

itoggle caption Frank Morris/KCUR

Ray Gerrish repairs a drilling rig near Watford City, N.D. Oil industry analysts predict that oil prices will have to remain low for at least several months before having a significant effect on U.S. production. Jim Gehrz/MCT/Landov hide caption

itoggle caption Jim Gehrz/MCT/Landov

Pumpjacks at the Inglewood oil fields in California in March. Some of the most controversial methods of oil extraction, like fracking, oil sands production and Arctic drilling, are also expensive. That's made them less profitable as the price of oil continues to fall. Richard Vogel/AP hide caption

itoggle caption Richard Vogel/AP

Guillermo Gomez, husband of Vilma Marenco, holds his daughter in their home in Northeast Houston. Marenco was killed in April after being hit by an uninsured trucker who ran a red light. Mayra Beltran/Houston Chronicle hide caption

itoggle caption Mayra Beltran/Houston Chronicle

When Dawn Gioia first received a request to lease mineral rights under her home, in a downtown neighborhood in Brighton, Colo., she thought it was a scam. Lesley McClurg/Colorado Public Radio hide caption

itoggle caption Lesley McClurg/Colorado Public Radio

At the Pittsburgh International Airport, Consol Energy will begin extracting gas — even under the runways. MeRyan/Wikimedia Commons hide caption

itoggle caption MeRyan/Wikimedia Commons

A worker stands on top of a storage bin on July 27, 2011, at a drilling operation in Claysville, Pa. The dust is from powder mixed with water for hydraulic fracturing. Keith Srakocic/AP hide caption

itoggle caption Keith Srakocic/AP