Description: This shapefile includes arcs and regions that describe U.S. Geological Survey defined petroleum resource Assessment Units of the World. Each assessment unit is defined as a mappable volume of rock within a total petroleum system that encompasses fields (discovered and undiscovered) that share similar geologic traits and socio-economic factors. The fields inside an assessment are a sufficiently homogenous population that a single methodology of resource assessment is applicable. Assessment units are described by U.S. Geological Survey research scientists on the basis of available geologic knowledge, exploration and production histories, and extensive literature searches. Assessment units are identified with a numeric code derived from the numeric code of the World Geologic Provinces defined by the U.S. Geological Survey World Petroleum Assessment 2000. Most assessment units are contained within a single geologic province, but there are numerous cases where units span more than one province. Summary results of the assessment are presented as attributes of this shapefile.