Focus on top spots to boost US oil output even as well permits fall
December 05, 2014 at 01:00 AM EST
WILLISTON, N.D./HOUSTON, Dec 5 (Reuters) - U.S. energy firms are swiftly shifting drilling rigs away from less productive areas and hunkering down in sweet spots of North Dakota and Texas shale oil fields as they try to lift output and cut costs in response to the toughest crude market in years.