The USGS Central Region Energy Team assesses oil and gas resources of the United States. The onshore and State water areas of the United States comprise 71 provinces. Within these provinces, Total Petroleum Systems are defined and Assessment Units are defined and assessed. Each of these provinces is defined geologically, and most province boundaries are defined by major geologic changes. The Hanna, Laramie, Shirley Basins Province is located in south-central Wyoming and north-central Colorado, encompassing all or parts of Larimer County in Colorado and all or parts of Albany, Carbon, Converse, and Natrona, Counties in Wyoming. The main population centers within the study area are Laramie and Rawlins Wyoming. The main highways are I-80, which traverses the area east to west and U.S. Highway 287, which generally traverses the area from north to south. The North Platte, Medicine Bow, and Laramie rivers and their tributaries drain the area. The province boundary was drawn to include the geologic structures generally considered to be in the Hanna, Laramie, and Shirley Basins.