points (¼ mile for “measured,” ¾ mile for “indicated,” 3 miles for “inferred,” and >3 miles for “hypothetical” reserves). The speculative category (Figure 3.1) applies where a geological setting that is likely to contain coal has not yet been explored. State geological surveys working in cooperation with the USGS have been encouraged to adopt this system.


The two primary federal agencies that provide resource and reserve information are the Energy Information Administration in the Department of Energy, and the U.S. Geological Survey in the Department of the Interior.

U.S. Energy Information Administration

The EIA is responsible for maintaining Demonstrated Reserve Base (DRB) data (Box 3.1), the basis for assessing and reporting U.S. coal reserves. The DRB evolved from work performed by the U.S. Bureau of Mines that was published as Information Circulars 8680 and 8693 (USBM, 1975a, 1975b). These circulars contain estimates of DRB tonnage remaining in 1971, reported by county and

BOX 3.1

U.S. Demonstrated Reserve Base (DRB)

The DRB is a collective term for the sum of coal in both “measured” and “indicated” resource categories (see Figure 3.1), and includes the following:

  • Beds of bituminous coal and anthracite 28 inches or more thick and beds of subbituminous coal 60 inches or more thick that can be surface mined; and

  • Thinner and/or deeper beds that presently are being mined or for which there is evidence that they could be mined commercially at this time.

The DRB represents that portion of the identified resources of coal from which reserves are calculated (see Figure 3.2) and is thus a derived value using arbitrary limits and based on limited coal industry data. More recent (2005) numbers for each category except total resources are presented in Table 3.1.

The concept that coal resource and reserve tonnages will sequentially decrease corresponding to greater data reliability and increased confidence in economic recoverability, as portrayed in Figure 3.2, is fundamentally correct. However, there is no justification for the estimates to have more than two significant figures, nor are the sharp boundaries between the different reserve and resource categories realistic. These boundaries will shift up or down (decreasing or increasing tonnage estimates) depending on the availability of new information or particular changes or trends in technology and economics, as well as environmental constraints, transportation availability, and demographic shifts.

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