The Williston Basin is a large basin in eastern Montana, western North and South Dakota, and southern Saskatchewan known for its rich deposits of petroleum and potash. The basin extends approximately 475 miles (764 km) north-south and 300 miles (480 km) east-west.
The long history of sedimentary deposition in the Williston Basin included deposition of rocks well suited to serve as hydrocarbon source and reservoir rocks. The basin’s oil and gas fields are found in a wide range of geologic ages.
Oil was first found in the Williston Basin along the Cedar Creek Anticline in southeastern Montana, in the 1920s and 1930s. The basin did not become a major oil province until the 1950s when large fields were discovered in North Dakota. Production peaked in 1986, but in the early 2000s significant increases in production began because of application of horizontal drilling techniques.
Cumulative basin production totals about 3.8 billion barrels (600,000,000 m3) of oil and 470 billion cubic feet (1.3×1010 m3) of natural gas.