USGS: Permian Secondary Shales Hold 1.6 Billion Barrels of Recoverable Oil
The new assessment also estimates 28.3 Tcf of technically recoverable gas in the Woodford and Barnett shales.
View of the Franklin Mountains in El Paso, Texas, which sits atop the Woodford Shale.
Source: Andrea Cicero/USGS.
The US Geological Survey (USGS) has released a new assessment for the Permian Basin showing that two secondary targets, the Woodford and Barnett shales, hold technically recoverable resources totaling 28.3 Tcf of natural gas and 1.6 billion bbl of crude oil. The agency noted that the two formations have been produced since the 1990s and have delivered about 26 million bbl of oil to date.
The new data extend prior USGS work to quantify the Permian’s shale resources.
In 2016, the Wolfcamp Shale in the Midland Basin was estimated to hold 20 billion bbl of oil, 16 Tcf of associated gas, and 1.6 billion bbl of natural gas liquids. On the Delaware Basin side of the Permian, a 2018 USGS assessment estimated technically recoverable resources of 46.3 billion bbl of oil and 281 Tcf of natural gas across the Wolfcamp and Bone Spring formations.
The assessment compares to the 2016 assessment of the Wolfcamp in the Midland Basin side of the Permian which came in at 20 billion bbl of oil, 16 Tcf of associated gas, and 1.6 billion bbl of natural gas liquids. On the Delaware Basin side of the Permian, the USGS said in 2018 that technically recoverable reserves were 46.3 billion bbl of oil and 281 Tcf of gas between the Wolfcamp shale and Bone Spring formation.
USGS said the organic-rich Woodford and Barnett are found at depths ranging from 18,000 to 20,000 ft, placing them deeper than most other resource targets in the Permian Basin.
“The US economy and our way of life depend on energy, and USGS oil and gas assessments point to resources that industry hasn’t discovered yet. In this case, we have assessed there are significant undiscovered resources in the Woodford and Barnett shales in the Permian Basin,” Ned Mamula, director of the USGS, said in a statement.
The Woodford has a maximum thickness of about 900 ft and is variably porous, with porosity as high as 10%, and is highly quartzose, according to the USGS. As of November 2025, production from the Woodford is concentrated along the margins of the Delaware and Midland basins and across structural highs on the Central Basin Platform.
Maps showing the locations of the Woodford and Barnett shales in the Permian Basin.
Source: US Geological Survey.
The Barnett has a maximum thickness of roughly 700 ft and is generally less porous, ranging from about 3 to 6%, than the Woodford. It is composed primarily of quartz and clays, with biogenic silica more prevalent to the south and detrital quartz more common to the north. Most activity is concentrated along the western edge of the basin, where thermal maturity, thickness, and drilling depth are more favorable for oil production.
A recent report from data and services provider TGS described the Barnett and Woodford as “compelling alternatives” to the more prolific Wolfcamp and Bone Spring formations. The report noted that, in addition to a shrinking inventory of untapped locations, production from the core plays has become increasingly water-intensive, with water-to-oil ratios rising by about 120% since 2005.
“While historically viewed as less productive, Barnett and Woodford generate significantly less water and show promising economic potential, particularly as existing infrastructure across the Midland Basin supports efficient development and reduced operating costs,” the TGS report said.
Diamondback Energy discussed the Barnett and Woodford during a November earnings call with investors, saying it is delineating the intervals and is encouraged by early results. The company said it expects to provide additional updates this year and believes the zones could represent Tier 1 resources within its portfolio.
Other Permian operators reported to be targeting the formations include ExxonMobil and Occidental, as well as smaller independents such as SM Energy, IOG Resources, Fasken Oil and Ranch, and Elevation Resources.
