Over 434 billion tons of total in-place coal resources
are estimated in Colorado to a maximum depth of 6,000 ft. This resource represents 11 percent of all in the United States, making Colorado 4th in total coal resources. Coal cannot be safely mined deeper than about 3,000 ft. Colorado's potentially mineable coal resources to this depth are nearly 129 billion tons. In terms of bituminous 'identified' coal Colorado ranks second to Illinois in this category, but is first in the nation in terms of low-sulfur bituminous coal. Available coal resources are those 'identified' resources that remain available to mine after subtracting coal lost in mining, land-use and environmental restrictions on the surface (such as towns and rivers), and technological and geologic restrictions (such as coal near faults and steeply dipping strata). It is estimated that Colorado has 30 billion tons of coal available for mining.
The number is much lower for coal reserves
. This is the amount of 'identified' coal that can be mined economically. That is, the coal with good rank, quality, and quantity sufficient for use and that can be mined at a profit under current market conditions. Colorado's demonstrated reserve base today is 16.0 billion tons of coal, which places us eighth highest in the nation.http://pubs.usgs.gov/bul/b1450b/b1450.htm
is a link to the US Geological Survey coal resource classification system.