The U.S. Geological Survey is conducting an investigation of the oil and gas potential of the existing and proposed wilderness areas for the western United States. These current assessments are based upon a Wilderness System containing approximately 105 million acres (42 million ha.) of land (80 million acres [32 million ha.] in existing wilderness; about 16 million acres [6.5 million ha.] in proposed wilderness; and another 9 million acres [3.5 million ha.] potential wilderness lands under study).

It is necessary to consider the uncertainty in the estimates of petroleum resources in the wilderness tracts due to the limited data and lack of detailed geologic information available for many of the areas. In light of these limitations, maps were compiled on a state-by-state basis which delineate: (1) the boundaries of the wilderness land categories for the Forest Service, National Park Service, Fish and Wildlife Service, and Bureau of Land

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Management; (2) the petroleum province boundaries of the U.S. Geological Survey Resource Appraisal Group as used in the 1981 national assessments; and (3) the geologic boundaries which distinguish the sedimentary-rock provinces having petroleum potential from the crystalline-rock provinces having no petroleum potential. All of the wilderness lands are digitized for mapping purposes and for calculation of the areas for each respective wilderness tract within the boundaries of the sedimentary-rock province. A computer search and compilation of exploratory-well data from the Petroleum Information Corp.'s Well History Control System (WHCS) was conducted for all the wilderness areas and their immediate surrounding. This tabulation of known well data is a part of the geologic input to the r source-assessment procedures.

Assumptions incorporated into the resource-appraisal methods are: (1) resource potential is not uniformly distributed throughout a petroleum province; (2) the total distribution of all recoverable petroleum resources is considered, both discovered and undiscovered; (3) consideration of the geologic characteristics favorable for the accumulation of petroleum resources in all the wilderness areas; (4) probability distributions are used to calculate a range of resource values to deal with the risks of uncertainty; and (5) the use of several alternative resource-appraisal methods are critically assessed.

The petroleum-resource assessments are compiled and reported by petroleum province and for each state. A total aggregation of the estimated petroleum resources for the existing and proposed wilderness areas in the 11 western states are presented as probability distributions.

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