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.
From left, Topher Jones, Edward Hartmann and Angie Holliday hold a campaign sign outside City Hall in Denton, Texas, on July 15, 2014. Voters in the college town approve a ban on fracking on Tuesday.
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.