The purpose of this documentation is to provide a detailed description of the models and methods used to assess future exploration and development of the domestic onshore undiscovered oil resource. The methodology was designed to be consistent with methods used in the Total Oil Recovery Information System (TORIS). This documentation provides details on data acquisition, analytical assumptions, data evaluation techniques, engineering analysis, economic evaluation, and timing algorithms used in these models to assess future oil exploration activities. The goal is to provide an overview of the full analytical system as developed and currently implemented by TORIS. The report outlines the general approach and data sources used in describing the resource remaining in undiscovered reservoirs nationwide. The analysis relies on the quantification of undiscovered resources developed by the U.S. Geologic Survey (USGS). The current description of the remaining undiscovered resource is defined by their assessment published in 1995 (1995 National Assessment of United States Oil and Gas Resources Results, Methodology, and Supporting Data). Reservoir properties are based on data gathered from existing oil reservoirs within individual plays. A database? of existing oil reservoirs was created by merging the existing TORIS database with databases created by NRG associates (NRG, 1993). Procedures have been established to allow easy updates to the system as new data become available. The incorporation of new or expanded assessments or new play characterization, can be readily handled in the existing structure. The modeling procedures include a comprehensive assessment method for determining the relative economics of various prospects based on future financial conditions, the nature of the undiscovered resource, prevailing risk factors, and the available technologies. The model evaluates the economics of exploration and development from the perspective of an operator making an investment decision. The individual accumulation is the unit of analysis for these models. The evaluation of each accumulation considers the full cost of developmental drilling and production. An accumulation, by definition, is the collection of all pools within a field within a given geologic play. The exploration evaluation considers both the size and frequency of undiscovered accumulations in order to determine the order of discovery within a play. Investment efficiency is used as the criteria in determining the order in which plays are explored. A timing model determines the development timing of each newly discovered accumulation on a sunk exploration cost basis constrained by capital and regional rig availability.