The Williston Basin is a large intracratonic sedimentary basin in eastern Montana, western North and South Dakota and southern Saskatchewan known for its rich deposits of petroleum and potash. The basin is a geologic structural basin but not a topographic depression; it is transected by the Missouri River. The oval-shaped depression extends approximately 475 miles (764 km) north-south and 300 miles (480 km) east-west.

The Bakken Formation is an oil-bearing stratum covering parts of Montana, North Dakota, and Saskatchewan. Oil was first produced from the Bakken more than 50 years ago. Production was mainly from a few vertical wells until the 1980's when horizontal or directional drilling technology became available. Only recently after the intensive application of horizontal wells combined with hydraulic fracturing technology did production really accelerate. The Bakken is one of many hydrocarbon producing formations in the Williston Basin, a sedimentary basin covering parts of three states and two provinces. The total layer of sediments in the basin can be up to 15,000 ft. thick, and within that, the Bakken itself reaches a maximum of 150 feet. The Bakken Shale is the largest oil find in the history of the U.S. according to the U.S. Geological Survey (USGS). Estimates are that the Bakken Formation contains approximately 167.0 billion barrels of oil, but only 3 to 43 billion barrels can be recovered with today's technology.

Deposition of sediments began in the Williston area during Cambrian time, but subsidence and basin filling were most intense during the Ordovician, Silurian and Devonian Periods, when thick accumulations of limestone and dolomite, with lesser thicknesses of sandstones, siltstones, shales, and evaporates were laid down approximately 350 to 417 million years ago. Subsidence continued on a reduced scale into the Mississippian and was largely ended by the Pennsylvanian time. Regional subsidence returned during the Mesozoic Era, although total sediment thicknesses were much less than during the Paleozoic. Near the end of the Cretaceous period, tectonic activity during the Laramide Orogeny rejuvenated several basement structures in the Williston Basin to produce anticlines that serve as oil traps today.

The Bakken Shale in the Williston Basin is over 11,000 ft deep at the center of the formation and rises to 3,100 ft. on the edges of the basin. The Bakken Formation is composed of three distinct members. The first layer averages twenty three feet in depth and consists of blackish marine shale. The second member which runs from 30 ft to 80 ft. and composed of interbedded limestone, siltstone, sandstone and dolomite. The bottom member is a dark black marine shale that averages 10 ft. to 30 ft. in thickness. All three formations that make up the Bakken are rich in an organic material called Kerogen. When Kerogen is heated (thermogenic processes) or broken down by organic means (biogenic processes), natural gas and oil are created. The Bakken Formation is capped by a very thick limestone formation called the Lodgepole. It is because of this limestone cap that there is so much gas and oil trapped in the shale horizons. The Bakken Formation is what is considered a thermally mature deposit and the oil from the Bakken has a 41 specific gravity and is deemed to be commercially high grade crude oil.