Since January 1997, weekly U.S. crude oil imports averaged near 9.2 million barrels a day, topping domestic output by 3.5 million barrels a day, or more than 60%.

Output from shale-oil fields in North Dakota and elsewhere, both in and out of the traditional oil patch, is gushing at more than one million barrels a day above a year ago. Hydraulic fracturing, horizontal drilling and other techniques are set to lift output by a further 1.3 million barrels a day by the end of 2014. Output will hit a 28-year high of near 8.6 million barrels a day, say government forecasters at the Energy Information Administration.

By the end of 2014, the current tiny trickle will widen to see domestic crude oil output topping imports by nearly 2.5 million barrels a day. A slow shift, 16 years in the making, is set to become a flood in little more than 16 months.