The D-J Basin, also known as the Denver-Julesburg Basin (after Julesburg, Colorado), is a geologic structural basin centered in eastern Colorado in the United States, but extending into southeast Wyoming, western Nebraska, and western Kansas. It underlies the Denver-Aurora Metropolitan Area on the eastern side of the Rocky Mountains.

The basin itself forms a petroleum province. Oil and gas have been produced from the Denver Basin since the discovery in 1901 of oil in fractured Pierre Shale at the McKenzie Well, part of the Boulder oil field in Boulder County.

Currently leasing
& buying in these
areas in the
D-J Basin:

The Williston Basin is a large basin in eastern Montana, western North Dakota, South Dakota, and southern Saskatchewan, that is known for its rich deposits of petroleum and potash.

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, especially in the Bakken Formation.