The Williston Basin Bakken petroleum system is a giant continuous accumulation. The petroleum system is characterized by low-porosity and -permeability reservoirs, organic-rich source rocks, and regional hydrocarbon charge. Total Bakken Formation and Three Forks Formation production to June 2019 is 3.3 billion bbl (0.52 billion m3) and 4.8 tcf of gas (0.135 trillion m3) from 19,075 wells. Daily production is over 1 million bbl (160,000 m3) per day.
The Bakken Formation regionally in the Williston Basin consists of four members: upper and lower organic-rich black shale, a middle member (silty dolostone or limestone to sandstone lithology), and a basal member recently named the Pronghorn. The Bakken Formation ranges in thickness from a wedge edge to more than 140 ft (42.6 m), with the thickest area in the Bakken located in northwest North Dakota, east of the Nesson anticline.
The Three Forks is a silty dolostone throughout much of its stratigraphic interval. The Three Forks ranges in thickness from less than 25 ft to more than 250 ft (7.6–76.2 m) in the mapped area. Thickness patterns are controlled by paleostructural features such as the Poplar Dome and Nesson, Antelope, Cedar Creek, and Bottineau anticlines. Thinning and or truncation occurs over the crest of the highs, and thickening of strata occurs on the flanks of the highs. The Three Forks can be subdivided into three units (up to six by some authors). Most of the development activity in the Three Forks targets the upper Three Forks.