Resources, Reserves, and DRBa
and other terms used by the Energy Information Administration.
Resources are naturally occurring concentrations or
deposits of coal in the Earth's crust, in such forms and
amounts that economic extraction is currently or potentially
Measured Resources refers to coal for which estimates of
the rank and quantity have been computed to a high degree of
geologic assurance, from sample analyses and measurements from
closely spaced and geologically well known sample sites. Under
the U.S. Geological Survey (USGS) criteria, the points of
observation are no greater than 1/2-mile apart (see Figure
A1). Measured coal is projected to extend as a 1/4-mile-wide
belt from the outcrop or points of observation or measurement.
Indicated Resources refers to coal for which estimates of
the rank, quality, and quantity have been computed to a
moderate degree of geologic assurance, partly from sample
analyses and measurements and partly from reasonable geologic
projections. Under the USGS criteria, the points of
observation are from ½ to 1½- miles apart (see Figure A1).
Indicated coal is projected to extend as a ½-mile-wide belt
that lies more than ¼mile from the outcrop or points of
observation or measurement.
Demonstrated Resources are the sum of measured resources
and indicated resources.
Demonstrated Reserve Base (DRB) (or just "reserve base" in
USGS usage) is, in its broadest sense, defined as those parts
of identified resources that meet specified minimum physical
and chemical criteria related to current mining and production
practices, including those for quality, depth, thickness,
rank, and distance from points of measurement. The "reserve
base" is the in-place demonstrated resource from which
reserves are estimated. The reserve base may encompass those
parts of a resource that have a reasonable potential for
becoming economically recoverable within planning horizons
that extend beyond those which assume proven technology and
Inferred Resources refers to coal of a low degree of
geologic assurance in unexplored extensions of demonstrated
resources for which estimates of the quality and size are
based on geologic evidence and projection. Quantitative
estimates are based on broad knowledge of the geologic
character of the bed or region where few measurements or
sampling points are available and on assumed continuation from
demonstrated coal for which there is geologic evidence. The
points of measurement are from 1½ to 6 miles apart (Figure
A1). Inferred coal is projected to extend as a 2¼-mile-wide
belt that lies more than ¾ mile from the outcrop or points of
observation or measurement. Inferred resources are not part of
Recoverable refers to coal that is, or can be, extracted
from a coalbed during mining.
Reserves relates to that portion of demonstrated resources
that can be recovered economically with the application of
extraction technology available currently or in the
foreseeable future. Reserves include only recoverable coal;
thus, terms such as "minable reserves," "recoverable
reserves," and "economic reserves" are redundant. Even though
"recoverable reserves" is redundant, implying recoverability
in both words, EIA prefers this term specifically to
distinguish recoverable coal from in-ground resources, such as
the demonstrated reserve base, that are only partially
Minable refers to coal that can be mined using present-day
mining technology under current restrictions, rules, and
aFor a full discussion of coal
resources and reserve terminology as used by EIA, USGS, and
BOM, see U.S. Coal Reserves, 1996, Appendix A,
Specialized Resource and Reserve Terminology.
Sources: U.S. Department of the Interior, Coal Resource
Classification System of the U.S. Bureau of Mines and the U.S.
Geological Survey, Geological Survey Bulletin 1450-B
(1976). U.S. Department of the Interior, Coal Resource
Classification System of the U.S. Geological Survey,
Geological Survey Circular 891 (1983) U.S. Department of the
Interior, A Dictionary of Mining, Mineral, and Related
Terms, Bureau of Mines (1968).
top of page