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Many factors influence the classification of coal, but the most useful is heat value, expressed in British Thermal Units (BTUs) per pound of coal burned. Although coal with high BTU levels often has high sulfur as well, the two are NOT necessarily related. Many coal deposits in the United States are both high in heat value and low in sulfur content.

Generally, the lowest BTU coals are the youngest in geological time. Many subclasses exist within the following general classifications, and the categories frequently overlap, depending upon other factors.

From about 6000 to over 7000 BTUs per pound. Relatively small deposits exist in Wyoming.

About 8,000 to 11,500 BTUs per pound. This coal forms by far the largest tonnage of Wyoming's demonstrated reserves. The principal deposit lies in the Powder River Basin.

10,500 to 14,000 BTUs per pound. Significant reserves of this coal exist in Wyoming, especially along the southern border.

Over 14,000 BTUs per pound. Little or no mineable reserves exist within Wyoming.

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Sulfur Content of coal has become at least as important as its BTU value since the advent of the Clean Air Act. Low sulfur is environmentally desirable However, "low sulfur" is a relative term. As a rule of thumb, coal which emits 1.2 pounds or less of sulfur per million BTUs of heat produced is called "low sulfur."

This was the original standard set by the Clean Air Act. Most Wyoming coal meets the "low sulfur" standard. In 1990, Congress enacted significant revisions to the Clean Air Act (CAA.) For Wyoming, the important point of these complex revisions is that they removed legal and artificial barriers to the use of its coal which had been enacted in the late 1970s. Wyoming appears to be experiencing a surge in coal sales as a result of the CAA revisions.

Last Update 01/28/01

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