Even though U.S. coal production remained strong over the past decade, coal is losing its share of overall U.S. energy production, primarily to natural gas. One of the big questions for the industry is how to penetrate the overseas coal market, particularly for steam coal, to compensate for declining domestic demand. In the past few years, coal production was at or near record levels and exports were up, while domestic demand declined. As U.S. energy policy and environmental regulations are constantly debated, there is ongoing congressional interest in the role of coal in meeting U.S. and global energy needs. The question may not be whether the domestic production of coal is here to stay but, rather, how much U.S. coal will be burned, what type, and under what regulatory framework. The gap between U.S. coal production and consumption may continue to widen as low cost natural gas becomes more attractive to power plants (at least in the short run) and as older coal plants idle or close and uncertainties with emission regulations potentially inhibit new coal plant investments. The Energy Information Administration (EIA) forecasts coal exports to continue to rise over their forecast period (2015-2040). Exports to the Asian market are expected to increase, but there are potential bottlenecks such as infrastructure (e.g., port development and transportation) that could slow export growth. Factors contributing to lower coal demand in the United States include low economic growth, high coal prices, lower natural gas prices, and coal plant retirements. Table 1 illustrates the current coal supply-demand balance. The coal industry is highly concentrated in the United States, with just a handful of major producers, operating primarily in four states, and the dominant holder of reserves (about one-third) being the U.S. government. Coal deposits (resources) are spread throughout the United States (see Figure1 ). There has been considerable congressional interest in coal, with over 100 bills that were introduced in the 112 th Congress many of which addressed environmental and worker safety issues, neither of which are covered in this report. The discussion below is intended to provide some background and context for potential coal debates during the 113 th Congress. This report serves as a primer on U.S. and world coal resources and production and highlights some of the congressional interest related to coal production on U.S. federal lands. The report primarily describes the past 10 years of coal activity but also includes a discussion of future coal production projections and federal coal incentives, many of which do not expire. Coal consists of the fossilized remains of ancient plant life that have been transformed through metamorphosis into carbon-rich mineral deposits. It occurs as seams in sedimentary rock strata as old as 300 million years, though the most abundant deposits in the United States were deposited during the geologic Carboniferous period between 210 and 250 million years ago. Coal mineral classification considers type, rank, and grade. The plant life that coal originated from determines its type, and the degree of metamorphosis determines its rank, grade, and the amount of inorganic mineral matter present. Qualities such as moisture, carbon, sulfur, and ash content contribute to a coal's heating value as a fuel (measured in British thermal units [Btus]). The content of sulfur is significant because of the sulfur dioxide (SO2) emissions that occur during coal combustion. Under the Clean Air Act, there are federal limits on the amount of SO 2 , among other pollutants, allowed from coal-fired power plants. Western coal (low sulfur and low energy content) primarily produced in the Powder River Basin (PRB) of Wyoming, is used generally for power generation, while eastern coal has been used domestically for power generation and exported for coking and metallurgical purposes. Moisture adds weight to the coal, increasing shipping costs while decreasing its heating value. Minerals deposited with the plants that formed coal create ash when coal burns. Table 2 below illustrates the various coal classifications. There are two primary mining techniques used in the United States: underground mining and surface mining. About 69% of U.S. coal comes from surface mines, while the remaining 31% comes from deep underground mines. There are two primary underground mining techniques: room and pillar (including conventional and continuous mining) and longwall. Room and pillar and continuous mining is practiced as follows: In flat-lying coal beds, conventional room and pillar techniques rely on cutting, drilling, blasting, loading, hauling, and roof bolting—a labor-intensive process. Long steel bolts properly spaced and driven into the roof are required. In continuous mining, the cutting, drilling, blasting, and loading are performed by a mechanical excavator known as a continuous miner. The continuous miner cuts and loads the coal. Together, room and pillar and continuous techniques account for 50% (conventional, room and pillar—2%; continuous—48%) of underground mining. The most efficient technique in underground mining is the longwall method, which employs a large machine with a rotating drum that moves back and forth across a wide coal seam. Once coal is removed by a longwall miner or other method, it is then moved out of the mine with conveyor belts or shuttle cars. About 50% of underground coal is produced using the longwall technique. Surface mining, also called "open-pit" or strip mining, entails blasting rock above the coal with explosives. This overburdened rock is then removed with huge electric shovels and draglines to reveal the coal seam. The coal seam in a surface mine is worked in long cuts by uncovering and removing coal then backfilling and reclaiming land in sequence. In other words, while coal extraction is taking place, as required by federal law, the reclamation work occurs in an adjacent area previously mined. Mountaintop removal mining is a form of strip mining. Mountaintop removal mining generally removes a coal seam from one side of a mountain to the other. This is typically done in "steep-terrain" surface mining. Some of the overburden or "excess spoil" from the top of the mountain is placed in a valley fill. The placement of the excess spoil in valleys adjacent to mining areas remains controversial. After being mined, coal goes through a cleaning prep facility, where it is cleaned and separated by grades. Cleaning upgrades the quality of the coal by removing some of the impurities such as rock, clay, and other ash-producing material. In the eastern United States, this refuse is generally pumped into an impoundment area often built near old underground mines in steeply sloping valleys. Once cleaned and separated, if necessary, the coal is stockpiled and shipped to the customer by rail, barge, truck, or conveyor. It usually takes more than one mode of transport for coal to reach its final destination. Utilities burn pulverized coal to produce high-pressure steam that powers an electric generator. As coal is burned, emissions are produced that contain sulfur dioxide, nitrogen oxides, carbon dioxide, particulate matter, ash, and mercury. A discussion of coal combustion emissions is found in other CRS reports. Assessing the amount of coal in the United States is quite complex. Two very different terms used to describe coal deposits—resources and reserves—are sometimes used interchangeably, but have very different meanings. Resources provide a broad measure of coal production potential, or amount of coal "in the ground" summing the identified and undiscovered deposits of a minimum thickness. Reserves are known quantities that can be produced given current prices and technology. Resource assessments are complex and rely on bed thickness as a major factor in determining recoverability, with direct correlation between bed thickness, depth, and recoverability. Coal rank (degree of metamorphism) and coal quality (heating value) contained in a unit of coal are factors as well. A February 2013 assessment by the U.S. Geological Survey (USGS) estimate the Powder River Basin coal resource alone at about 1.07 trillion short tons. A National Research Council (NRC) study cautions that it is not sufficient to know there is a vast resource base in the United States because only a small amount can be mined economically (the reserves) and advises caution when using coal resources to estimate the life of the U.S. coal base. Resources, however, can become reserves. Reserve data is temporary and subject to change based on public policy, coal versus natural gas prices, production rates, transportation issues, exports, technology, and other conditions. Reserves are only an estimate of what might be recovered. Reserves must be developed from a better defined resource base according to the Virginia Center for Coal and Energy Research report. A maturity index is used to measure the ratio of the amount of remaining economically recoverable resources to the previously mined tonnages. The Interior and Appalachian regions have less than a 0 index meaning their recoverable reserves are less than the amount already mined. Those areas are far more developed than the western regions. The remaining eastern resources may be thinner and of lower quality overall, which may lead to more mining underground than before because much of the surface resources have already been mined. The United States has the largest amount of coal reserves and resources in the world. The U.S. Energy Information Administration (EIA) estimates there are about 261 billion short tons of recoverable domestic coal reserves. The total demonstrated resource base (DRB) is estimated at about 484.5 billion tons. EIA statistics show that more than half (55%) of U.S. coal reserves are located in the West, of which Montana and Wyoming together account for 43% (see Table 3 ). When including the top five producing states (three of which are in the East), 70% of U.S. coal reserves are accounted for.