The National Petroleum Reserve in Alaska (NPRA) is an area of land on the Alaska North Slope owned by the United States federal government and managed by the Department of the Interior, Bureau of Land Management (BLM). It lies to the west of the Arctic National Wildlife Refuge, which, as a U.S. Fish and Wildlife Service managed National Wildlife Refuge, is also considered federal land.
At a size of 23,599,999 acres (9,550,581 hectares; 36,875 square miles), the NPRA is the largest tract of undisturbed public land in the United States.Inupiat live in several villages around its perimeter, the largest of which is Barrow, the seat of the North Slope Borough.
An assessment by the United States Geological Survey (USGS) in 2010 estimated that the amount of oil yet to be discovered in the NPRA is only one-tenth of what was believed to be there in the previous assessment, completed in 2002. The 2010 USGS estimate says the NPRA contains approximately "896 million barrels of conventional, undiscovered oil". The reason for the decrease is because of new exploratory drilling, which showed that many areas that were believed to hold oil actually hold natural gas.
The estimates of the amount of undiscovered natural gas in the region also fell, from "61 trillion cubic feet of undiscovered, conventional, non-associated gas" in the 2002 estimate, to 53 trillion cubic feet (1,500 km3) in the 2010 estimate.
The NPRA was created by President Warren G. Harding in 1923 as Naval Petroleum Reserve Number 4 during a time when the United States was converting its Navy to run on oil rather than coal. In 1976 the Naval Petroleum Reserves Production Act (NPRPA) renamed the reserve the "National Petroleum Reserve in Alaska" and transferred it from the Navy to the Department of the Interior. The 1980 Interior Department Appropriations Act directed the Bureau of Land Management (BLM) within the Department of Interior to conduct oil and gas leasing. Nevertheless, the area was left essentially as a wilderness until the late 1990s.