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Coal takes millions of years to form

Coal is a combustible black or brownish-black sedimentary rock with a high amount of carbon and hydrocarbons. Coal is classified as a nonrenewable energy source because it takes millions of years to form. Coal contains the energy stored by plants that lived hundreds of millions of years ago in swampy forests.

Layers of dirt and rock covered the plants over millions of years. The resulting pressure and heat turned the plants into the substance we call coal.

Three images showing how coal was formed. The first image is of a swamp, 300 million years ago. Before the dinosaurs, many giant plants died in swamps.

The second image is of water, 100 million years ago. Over millions of years, these plants were buried under water and dirt.

The third image is of rocks and dirt over the coal. Heat and pressure turned the dead plants into coal.

Types of coal

Coal is classified into four main types, or ranks: anthracite, bituminous, subbituminous, and lignite. The ranking depends on the types and amounts of carbon the coal contains and on the amount of heat energy the coal can produce. The rank of a coal deposit is determined by the amount of pressure and heat that acted on the plants over time.

Anthracite contains 86%–97% carbon and generally has the highest heating value of all ranks of coal. Anthracite accounted for less than 1% of the coal mined in the United States in 2017. All of the anthracite mines in the United States are in northeastern Pennsylvania. Anthracite is mainly used by the metals industry.

Bituminous coal contains 45%–86% carbon. Bituminous coal in the United States is between 100 million and 300 million years old. Bituminous coal is the most abundant rank of coal found in the United States, and it accounted for about 46% of total U.S. coal production in 2017. Bituminous coal is used to generate electricity and is an important fuel and raw material for making iron and steel. West Virginia, Illinois, Pennsylvania, Kentucky, and Indiana were the five main bituminous coal-producing states in 2017, accounting for 74% of total bituminous production.

Subbituminous coal typically contains 35%–45% carbon, and it has a lower heating value than bituminous coal. Most subbituminous coal in the United States is at least 100 million years old. About 45% of total U.S. coal production in 2017 was subbituminous and nearly 89% was produced in Wyoming.

Lignite contains 25%–35% carbon and has the lowest energy content of all coal ranks. Lignite coal deposits tend to be relatively young and were not subjected to extreme heat or pressure. Lignite is crumbly and has high moisture content, which contributes to its low heating value. Lignite accounted for 9% of total U.S. coal production in 2017, and about 50% was mined in Texas and 43% in North Dakota. Lignite is mostly used to generate electricity. A facility in North Dakota also converts lignite to synthetic natural gas and pipes it to natural gas consumers in the eastern United States.

Last updated: November 26, 2018

Coal statistics

Data for the United States and for 2017 except where noted.

774.61 million short tons
716.96 million short tons
Coal consumption by end-use sector  
  Electric power sector
  Other industrial
  Coke plants
664.75 million short tons
  33.61 million short tons
  17.54 million short tons
    1.06 million short tons
Year-end coal stocks
163.54 million short tons
Average sales price
$33.72 per short ton
Average delivered price
  Electric power
 $39.09 per short ton
  Coke plants
$122.14 per short ton
  Other industrial plants
 $58.67 per short ton
Largest producing state
Wyoming—316.45 million short tons
Share of U.S. total produced in Western region 56%
Share of U.S. total produced from surface mining 65%
Demonstrated reserve base 475.9 billion short tons (as of January 1, 2017)
  7.78 million short tons
 96.95 million short tons
Consumption for total electricity generation
663.91 million short tons (93% of total U.S. coal consumption)
Coal share of total utility-scale electricity generation
Top five coal-consuming states by electric power sector  
 93.49 million short tons
 39.51 million short tons
 35.55 million short tons
 34.22 million short tons
 28.52 million short tons
Coal share of utility-scale electricity generating capacity (2017)
Largest producing coal mine
North Antelope Rochelle Mine/Peabody Powder River Mining LLC
101.59 million short tons, 13% of total U.S. production
Leading producing company
Peabody Energy Corporation
156.73 million short tons, 20% of total U.S. production
Average number of coal mining industry employees during the year
6.5 tons/miner-hour
1.8 tons/miner-hour
World coal production (2016)
8,199.98 million short tons
World coal consumption (2016)
8,384.18 million short tons

Last updated: November 9, 2018