Six formations in the Permian Basin of West Texas and New Mexico have made the region the nation’s leading oil breadbasket based on production, according to the U.S. Energy Information Administration (EIA).

The six formations — Spraberry, Wolfcamp, Bone Spring, Glorieta, Yeso and Delaware — provided the bulk of the basin’s 60% increase in oil output since 2007. Crude production in the Permian has grown from a low of 850,000 b/d in 2007 to 1.35 million b/d last year, according to EIA. Production from the six leading formations has helped drive the increase in Permian oil production, particularly since 2009, despite declining production from legacy wells.

Permian crude production has exceeded production from the federal offshore Gulf of Mexico region since March 2013, making the Permian the largest crude oil producing region in the United States, EIA said Wednesday.

Almost three-quarters of the production increase came from the Spraberry, Wolfcamp, and Bone Spring formations. Counties in these three formations have driven growth in the play’s horizontal oil-directed rig activity in recent months. “Production from these three formations collectively increased from about 140,000 b/d in 2007 to an estimated 600,000 b/d in 2013, increasing their share of total Permian oil production from 16% to 44%,” EIA said.

The Delaware and adjacent Glorieta and Yeso formations also charted production increases from 2007 to 2013, but to a lesser extent, EIA said. Production from these three formations rose from 61,000 b/d in 2007 to an estimated 112,000 b/d in 2013.

In recent months, the number of horizontal drilling rigs targeting oil in the Permian has climbed by more than five dozen, according to EIA, marking a steep ramp-up in activity.

At the start of last year, the Eagle Ford Shale and the Williston Basin had more oil-directed horizontal rigs than the Permian. But by the end of 2013, the 215 rigs in the Permian topped the Eagle Ford (173 rigs) and Williston (164 rigs). “During the first quarter of 2014, the increase in oil-directed horizontal rigs in the Permian Basin was more than four times the combined increase in the Eagle Ford and Williston Basin,” EIA said recently (see Shale Daily, May 15).

The Permian Basin region is about 250 miles wide and 300 miles long, and it contains many potentially productive low-permeability oil formations. Although oil production has previously come from the more permeable portions of the Permian formations, horizontal drilling and hydraulic fracturing have opened large and less-permeable portions to commercial production. This is especially true for the Spraberry, Wolfcamp, and Bone Spring formations, which have initial well production rates comparable to those found in the Bakken and Eagle Ford shales, EIA said.