Because the US has the world's largest coal reserves, it has sometimes been called "the Saudi Arabia of coal." It is the world's second-largest coal producer, after China, but surpasses both the number three and four producer nations (India and Australia) by nearly a factor of three.

Wood was this nation's primary fuel until the mid-1880s, when deforestation necessitated greater reliance on abundant coal resources. Coal then remained America's main energy source until the 1930s, when it was overtaken by oil. Today coal fuels about 50 percent of US electricity production and provides about a quarter of the country's total energy.

The US currently produces over a billion tons of coal per year, with quantities increasing annually. This is well over double the amount produced in 1960. However, due to a decline in the average amount of energy contained in each ton of coal produced (i.e., declining resource quality), the total amount of energy flowing into the US economy from coal is now falling, having peaked in 1998. This decline in energy content per unit of weight (also known as "heating value") amounts to more than 30 percent since 1955. It can partly be explained by the depletion of anthracite reserves and the nation's increasing reliance on sub-bituminous coal and even lignite, a trend that began in the 1970s. But resource quality is declining even within each coal class.

While there are coal resources in many states, the main concentrations are in Appalachia, Illinois, Wyoming, and Montana (see map below). The 53 largest coalmines in the US, located in just a few states, account for almost 60 percent of total production.

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(Note: This article is a draft chapter from a forthcoming book, currently titled Coal's Future/Earth's Fate, to be published by Post Carbon Press in spring 2009. The author wishes to thank Werner Zittel, David Rutledge, Jean Laherrère, David Strahan, Julian Darley, and Jason Brenno for assistance with this article.

Previous MuseLetters on global coal supply issues are archived on Global Public Media (www.globalpublicmedia.com) at MuseLetter 193: It's Happening, MuseLetter 190: The Great Coal Rush (And Why It Will Fail), and MuseLetter 179: Burning the Furniture).