More than 70% of the mean undiscovered oil resources is estimated to occur in five provinces: Arctic Alaska, Amerasia Basin, East Greenland Rift Basins, East Barents Basins, and West Greenland–East Canada. It is further estimated that approximately 84% of the undiscovered oil and gas occurs offshore. The USGS did not consider economic factors such as the effects of permanent sea ice or oceanic water depth in its assessment of undiscovered oil and gas resources. This assessment is lower than a 2000 survey, which had included lands south of the arctic circle.