coal bed and by sulfur content. The EIA became responsible for maintaining the DRB database in 1977 under the Department of Energy Organization Act of 1977 (P.L. 95-91), which required the EIA to carry out a comprehensive and unbiased data collection program and to disseminate economic and statistical information to represent the adequacy of the resource base to meet near- and long-term demands. Since 1979, EIA has published updates to the DRB by adding additional reserve/resource data from state coal assessments and by depleting the DRB according to the amount of annual coal production. The DRB represents a subset of total national coal resources, because it includes only coal that has been mapped, that meets DRB reliability and minability criteria, and for which the data are publicly available (see Box 3.1 and Figure 3.2). The EIA also reports Estimated Recoverable Reserves (ERR). The ERR is derived from the DRB by applying coal mine recovery and accessibility factors by state to the DRB. The ERR is categorized by state, Btu (British thermal unit) value, sulfur content, and mining type—it is the most widely reported and frequently quoted estimate of U.S. coal reserves.

FIGURE 3.2 Triangle depicting U.S. coal resources and reserves, in billion short tons, as of January 1, 1997. The darker shading corresponds to greater relative data reliability. SOURCE: EIA (1999).

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