Bituminous is the most abundant coal found in the United States, and is accounted for more than 50% of the coal reserves in the U.S. Bituminous Coal is a dark, hard like coal and its primary use is to generate electricity. Bituminous coal is the fastest growing market for coal in the U.S. Bituminous coal has a carbon content ranging from 43 to 87 percent and a heat value of 10,500 to 15,500 BTUs (British Thermal Unit). Bituminous coals are often subdivided depending on their heat value. Bituminous is classified as low, medium, and high volatile bituminous and subbituminous.