The total resource base in the United States, both renewable and non-renewable, is very large, with an energy content of over 657,000 billion barrels of oil equivalent (BBOE), or nearly 50,000 times the annual current rate of national energy consumption. Figure 1 shows graphically what the total resource base looks like, and in descending order, the values for the estimated accessible geothermal resource and estimated developable resource.
Energy resources are traditionally classified according to the degree of certainty and the economic feasibility of exploiting the particular resource. The U.S. Geological Survey (USGS) and the U.S. Department of Energy (DOE) have used such identifying terms for resource classification. Following are simple definitions of these classification terms: