Coal deposits come from many epochs, but the best and most abundant are from the forests in the warm, swampy river deltas of the Carboniferous period, some 320 million years ago.

Long before the dinosaurs reigned, there was a time ruled by forests of giant ferns, reeds, and mosses. The earth was a warmer, steamier place back then and plants thrived, growing taller than our tallest trees today.

As these plants died, they fell into the swampy waters to form rich layers of peat. These layers were typically sandwiched between layers of sediment like shale, deposited when waters temporarily retreated. During the Permian period, about 290 million years ago, the seas receded entirely, and many coastal plains turned to desert. Sedimentary rocks like sandstone were laid down over the shale and peat. Later, limestone was laid down when the waters returned.

In time, the weight of the upper layers pressed down on the lower layers, causing tremendous pressure and heat. This triggered chemical changes in the peat, forcing out oxygen and hydrogen and leaving behind rich deposits of carbon, called coal.

The deeper the coal, the more pressure was exerted on it. This caused different grades of coal—from hard, pure anthracite to softer lignite. Between these layers lay bituminous coal, which is used in today's electric utility power plants. Coal-based electricity provides 56% of America's electricity.

The four types (or "ranks") of coal mined today are: anthracite, bituminous, subbituminous, and lignite.

• Lignite: The largest portion of the world's coal reserves is made up of lignite, a soft, brownish-black coal that forms the lowest level of the coal family. You can even see the texture of the original wood in some pieces of lignite that is found west of the Mississippi River in the United States.
• Subbituminous: Next up the scale is subbituminous coal, a dull black coal. It gives off a little more energy (heat) than lignite when it burns. It is mined mostly in Montana, Wyoming and a few other western states.
• Bituminous: Still more energy is packed into bituminous coal, sometimes called "soft coal." In the United States, it is found primarily east of the Mississippi River in midwestern states like Ohio and Illinois and in the Appalachian mountain range from Kentucky to Pennsylvania.
• Anthracite: Anthracite is the hardest coal and gives off a great amount of heat when it burns. Unfortunately, in the United States, as elsewhere in the world, there is little anthracite coal to be mined. The U.S. reserves of anthracite are located primarily in Pennsylvania.

A Brief History of Coal Use

Coal is the most plentiful fuel in the fossil family and it has the longest and, perhaps, the most varied history. Coal has been used for heating since the cave man. Archeologists have also found evidence that the Romans in England used it in the second and third centuries (100-200 AD).

In the 1700s, the English found that coal could produce a fuel that burned cleaner and hotter than wood charcoal. However, it was the overwhelming need for energy to run the new technologies invented during the Industrial Revolution that provided the real opportunity for coal to fill Its first role as a dominant worldwide supplier of energy.

In North American, the Hopi Indians during the 1300s in what is now the U.S. Southwest used coal for cooking, heating and to bake the pottery they made from clay. Coal was later rediscovered in the United States by explorers in 1673. However, commercial coal mines did not start operation until the 1740s in Virginia.

The Industrial Revolution played a major role in expanding the use of coal. A man named James Watt invented the steam engine which made it possible for machines to do work previously done by humans and animals. Mr. Watt used coal to make the steam to run his engine.

During the first half of the 1800s, the Industrial Revolution spread to the United States. Steamships and steam-powered railroads were becoming the chief forms of transportation, and they used coal to fuel their boilers.

In the second half of the 1800s, more uses for coal were found.

During the Civil War, weapons factories were beginning to use coal. By 1875, coke (which is made from coal) replaced charcoal as the primary fuel for iron blast furnaces to make steel.

The burning of coal to generate electricity is a relative newcomer in the long history of this fossil fuel. It was in the 1880s when coal was first used to generate electricity for homes and factories.

Long after homes were being lighted by electricity produced by coal, many of them continued to have furnaces for heating and some had stoves for cooking that were fueled by coal.

Coal is our most abundant fossil fuel. The United States has more coal than the rest of the world has oil. There is still enough coal underground in this country to provide energy for the next 200 to 300 years.

Mining the Coal

Coal miners use giant machines to remove coal from the ground. They use two methods: surface or underground mining. Many U.S. coal beds are very near the ground's surface, and about two-thirds of coal production comes from surface mines.  Modern mining methods allow us to easily reach most of our coal reserves. Due to growth in surface mining and improved mining technology, the amount of coal produced by one miner in one hour has more than tripled since 1978.

Surface mining is used to produce most of the coal in the U.S. because it is less expensive than underground mining. Surface mining can be used when the coal is buried less than 200 feet underground. In surface mining, giant machines remove the top-soil and layers of rock to expose large beds of coal. Once the mining is finished, the dirt and rock are returned to the pit, the topsoil is replaced, and the area is replanted.

Underground mining, sometimes called deep mining, is used when the coal is buried several hundred feet below the surface. Some underground mines are 1,000 feet deep. To remove coal in these underground mines, miners ride elevators down deep mine shafts where they run machines that dig out the coal.

World Recoverable Coal Reserves (Billion Short Tons)

Although coal deposits are widely distributed, 67 percent of the world’s recoverable reserves are located in four countries: the United States .

Credit: BP Statistical review of world energy June 2007

United States Coal Reserves

Coal Production by Coal-Producing Region, 2005 (Million Short Tons and Percent Change from 2004)

Coal reserves are beds of coal still in the ground waiting to be mined. The United States has the world's largest known coal reserves, about 275 billion short tons. This is enough coal to last over two hundred years at today's level of use. Coal production is the amount of coal that is mined and sent to market. The United States produces over a billion short tons of coal each year, over 1/5 of the world's coal. 

Coal is mined in 27 states. Wyoming mines the most coal, followed by West Virginia, Kentucky, Pennsylvania, and Texas. Coal is mainly found in three large regions, the Appalachian Coal Region, the Interior Coal Region, and Western Coal Region (includes the Powder River Basin).

Appalachian Coal Region: 

• Annually produces about 35% of total U.S. coal production.
• Large underground mines and small surface mines.
• Coal mined in the Appalachian coal region is primarily used for steam generation for electricity, metal production, and for export.

Interior Coal Region: 

• Annually produces approximately 13% of total U.S. coal production.
• Mid-sized surface mines.
• Mid- to large-sized companies.

Western Coal Region: 

• Annually produces about 52% of total U.S. coal production.
• The State of Wyoming (number one coal state) accounts for over 30% of total U.S. coal production.
• Large surface mines.
• Largest coal mines in the world.

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credit: Energy Information Administration, U.S. Department of Energy, World Coal institute, OPEC, Shell Oil company