U.S.

Associated Press
In this Friday, July 20, 2012 photo, pipe for a pipeline is readied for installation near a drilling rig, near Calumet, Okla. Oklahoma is one of several states, including North and South Dakota, that has enjoyed a boom in the energy sector driven in large part by new and improved drilling techniques such as horizontal drilling and hydraulic fracturing, which cracks open fissures in rock formations to retrieve oil and gas. (AP Photo/Sue Ogrocki)

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