The Permian Basin produced 1.35 million barrels of oil per day (bbl/d) last year, with the bulk of the production coming from only six formations, according to a new report from the Energy Information Administration (EIA). Three of those formations--the Spraberry, Wolfcamp and Bone Spring--accounted for 75% of the increase in production.

“Counties in these three formations have driven the increase in the Permian Basin's horizontal, oil-directed rig activity in recent months,” according to the EIA. “Production from these three formations collectively increased from about 140,000 bbl/d in 2007 to an estimated 600,000 bbl/d in 2013, increasing their share of total Permian oil production from 16% to 44%.”

The other three formations--the Delaware, Glorieta and Yeso--also increased production from 2007 to 2013. “Production from these three formations rose from 61,000 bbl/d in 2007 to an estimated 112,000 bbl/d in 2013,” according to the report.

In 2013, the Permian accounted for 18% of total U.S. crude oil production. Since March of that year, crude oil production from the region has exceeded production from the federal offshore Gulf of Mexico. The region’s exponential growth has made the Permian Basin the largest crude oil producing region in the United States.