The U.S. Geological Survey completed an assessment of the undiscovered oil and gas potential of the Powder River Basin in 2006. The assessment of undiscovered oil and gas used the total petroleum system concept, which includes mapping the distribution of potential source rocks and known petroleum accumulations and determining the timing of petroleum generation and migration. Geologically based, it focuses on source and reservoir rock stratigraphy, timing of tectonic events and the configuration of resulting structures, formation of traps and seals, and burial history modeling. The total petroleum system is subdivided into assessment units based on similar geologic characteristics and accumulation and petroleum type. In chapter 1 of this report, five total petroleum systems, eight conventional assessment units, and three continuous assessment units were defined and the undiscovered oil and gas resources within each assessment unit quantitatively estimated. Chapter 2 describes data used in support of the process being applied by the U.S. Geological Survey (USGS) National Oil and Gas Assessment (NOGA) project. Digital tabular data used in this report and archival data that permit the user to perform further analyses are available elsewhere on this CD-ROM. Computers and software may import the data without transcription from the Portable Document Format files (.pdf files) of the text by the reader. Because of the number and variety of platforms and software available, graphical images are provided as .pdf files and tabular data are provided in a raw form as tab-delimited text files (.tab files).