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 Denver Basin Province is located in eastern Colorado, western Nebraska, southern South Dakota, and eastern Wyoming encompassing all or parts of Pueblo, El Paso, Crowley, Lincoln, Kit Carson, Elbert, Teller, Douglas, Jefferson, Denver, Arapahoe, Adams, Washington, Yuma, Morgan, Weld, Broomfield, Boulder, Larimer, Logan, Sedwick, Freemont, and Phillips Counties in Colorado. All or parts of Cheyenne, Deuel, Kimball, Banner, Scotts Bluff, Morrill, Garden, Sheridan, Box Butte, Sioux, and Dawes Counties in Nebraska. All or parts of Laramie, Platte, and Goshen Counties in Wyoming, and all of parts of Custer, Fall River, and Shannon Counties in South Dakota. The main population centers within the study area are Denver, Colorado Springs, Fort Collins, and Greeley Colo.; Cheyenne, Wyoming, and Scottsbluff, Nebraska. The main highways, I-70 and I-80 generally traverse the area from east to west, while I-25 generally traverse the area from north to south. The province boundary was drawn to include the geologic structures generally considered to be in or bounding the Denver Basin.