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 Williston Basin Province is located in North Dakota, eastern Montana, and northwestern South Dakota, encompassing all or parts of Divide, Burke, Renville, Bottineau, Rolette, Towner, Cavalier, Pembina, Walsh, Grand Forks, Nelson, Ramsey, Benson, Eddy, Foster, Wells, Griggs, Steele, Traill, Cass, Barnes, Ransom, Richland, Sergeant, Dickey, Lamoure, Logan McIntosh, Emmons, Burleigh, Kidder, Stutsman, Sheridan, McLean, Mountrail, Ward, McHenry, Pierce, Williams, McKenzie, Dunn, Mercer, Oliver, Morton, Sioux, Grant, Adams, Hettinger, Bowman, Slope, Golden Valley, Billings counties North Dakota and all or parts of Valley, Daniels, Sheridan, Roosevelt, Richland, Dawson, McCone, Wibaux, Prairie, Fallon, Custer, Carter, Garfield counties, Montana, and Harding, Butte, Lawrence, Pennington, Haakon, Jackson, Jones, Stanley, Ziebach, Dewey, Perkins, Corson, Campbell, Walworth, McPherson, Edmunds, Potter, Sully, Hughes, Stanley, and Meade counties South Dakota. The main population centers within the study area are Minot, Fargo, Grand Forks, and Bismarck, North Dakota; and Rapid City and Pierre, South Dakota. The main highways, I-94 and I-90, generally traverse the area from east to west. The Missouri River and its tributaries drain the area. The province boundary was drawn to include the geologic structures generally considered to be in or bounding the Williston Basin.