The Midland Basin of the Wolfcamp Shale area in the Permian Basin is now estimated to have 20 billion barrels of oil and 1.6 billion barrels of natural gas, according to a new assessment by the USGS.

That makes it three times larger than the assessment of the oil in the mammoth Bakken formation in North Dakota.

The estimate would make the oilfield, which encompasses the cities of Lubbock and Midland — 118 miles apart — the largest “continuous oil” discovery in the United States, according to the USGS.