Estimating resources of crude oil and natural gas contained in inadequately explored regions is fraught with difficulty. An analog method that I have used is described as follows.

1. Compute the total oil and gas resources originally in place in the intensively explored parts of the United States on the basis of (a) past production, (b) proved reserves, (c) future revisions of proved reserves, (d) future extensions of known pools, (e) additions in pools to be discovered in the course of development drilling, and (f) subcommercial accumulations or penetrated but undetected deposits that will be brought into production in the future.

2. Divide this explored area into a graded series of categories of total potential in barrels per 1,000 sq mi (2,590 km²).

3. Classify the various parts of the inadequately explored areas of the world into similar categories on the basis of past production and proved reserves (if any) and geologic characteristics.

4. Measure the area in each category in the inadequately explored region and multiply by the factor established for the geologically similar explored area.

Much of this procedure is based on available factual data, but the ratings of both the explored and the inadequately explored areas based on geologic factors are, to a large degree, subjective, and so is the decision as to what constitutes adequate exploration. To permit more complete judgment of the procedure, a map of the sedimentary basins of the world currently is being prepared for publication.