An economic appraisal was made of the oil potential of more than 80 producing fields in the Williston basin of Montana, North Dakota, and South Dakota. The major oil producing formations investigated were in the Mississippian, Devonian, Silurian, and Ordovician.

Data for the study came from field production and drilling statistics. An extrapolated oil production decline curve for a theoretical "average" producing well first was made for each field. The value of the total extrapolated amount of producible oil for the average well was then calculated, discounted for royalty, taxes, etc, and divided by the estimated cost for a completed producing well. This gave an estimate of the return per dollar invested. No considerations were given for exploration and land acquisition costs.

The estimated return per dollar values, after posting on Williston basin geologic maps, show relative economic comparisons of producing formations and where within the basin the best economic returns can be expected.

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