A geologic and economic appraisal was made of the oil potential of the Williston Basin of Montana, North Dakota and South Dakota. The major producing intervals investigated were the Ordovician, Devonian and Mississippian.

Data for the appraisal came from field and drilling statistics and geologic studies of more than eighty producing oil fields.

An extrapolated oil production decline curve was first constructed for a theoretical “average” producing well for each field. From this an estimated economic return was calculated which included cost of drilling and discounting for royalty, taxes, etc. No considerations were made for exploration and land acquisition costs.

The estimated returns, after posting on Williston Basin geologic maps, showed a relative geologic and economic appraisal of the major Ordovician, Devonian and Mississippian formations within the basin and where the best economic returns might be expected.