The Assessment Unit is the fundamental unit used in the World Petroleum Resources Project. The Assessment Unit is defined within the context of the higher-level Total Petroleum System. The Assessment Unit is shown here as a geographic boundary interpreted, defined, and mapped by the geologist responsible for the province and incorporates a set of known or postulated oil and (or) gas accumulations sharing similar geologic, geographic, and temporal properties within the Total Petroleum System, such as source rock, timing, migration pathways, trapping mechanism, and hydrocarbon type. The Assessment Unit boundary is defined geologically as the limits of the geologic elements that define the Assessment Unit, such as limits of reservoir rock, geologic structures, source rock, and seal lithologies.  
Purpose:
The purpose of these files is to define and illustrate the geographic limit and geologic boundaries of the Assessment Units within the defined Total Petroleum Systems, as required for the USGS World Petroleum Resources Project. The Assessment Units were used as the fundamental units for the assessment of undiscovered oil and gas. The assessment unit boundaries define the combined geologic limits of each Assessment Unit and are described and defined in the text portions of this assessment publication.