It is found in the Gulf Coast and Northern Plains regions of the United States. It is used primarily to generate electricity and to produce synthetic natural gas and liquids. Lignite reserves account for about 9 percent of the United States' coal reserves. These classifications are based on the amount of carbon, oxygen and hydrogen present in the coal. The amounts vary with the location of the coal seam, the types of plants from which the coal was formed, and the degree of change brought about by heat and pressure, often associated with the age of the coal.
All coal has carbon and sulfur to some degree.
HIGH - Coal containing 1.68 pounds of sulfur and above per million Btu.