Add this to the massive natural geological formations for potential shale gas and you have a much cleaner and cheaper fuel that could sustain the largest economies for over a century.

Fracking technology has already made it practical to exploit previously inaccessible natural gas and oil in the United States (see "Natural Gas Changes the Energy Map"). Now several companies are demonstrating a way to use microörganisms that eat coal and excrete methane—the main ingredient in natural gas—as a possible means of extracting fuel from coal resources that had been too expensive to mine.

Many coal beds contain large amounts of methane that can be harvested by drilling wells. In recent decades, researchers have demonstrated that a large fraction of the natural gas found in the coal beds is produced by naturally occurring microörganisms that feed on coal, and they have found ways to stimulate the microbes to produce more methane. Luca Technologies, based in Golden, Colorado, is using this approach to increase production from coal beds with existing methane wells. Another company, Next Fuel, based in Sheridan, Wyoming, recently showed that it could use similar technology to produce methane from coal beds that didn't already have methane in them, raising the possibility that vast amounts of coal that's currently too expensive to mine could be converted into natural gas.