Approximately 90 percent of natural gas is composed of methane, but it also contains small amounts of other gases such as propane and butane. Natural gas may also come from several other sources. One source is the gas found in coalbeds. Until recently, coalbed gas was just, considered a safety hazard to miners, but now it is a valuable source of natural gas. Another source of natural gas is the gas produced in landfills.
Landfill gas is considered a renewable source of natural gas since it comes from decaying garbage.
The gas from coalbeds and landfills accounts for three percent of the total gas supply today, yet their contribution could double by the year 2010. Altogether, the United States produces nearly 22 percent of the world's natural gas each year. In 1994 the United States imported 12 percent of its natural gas from other countries-mostly from Mexico and Canada. Usually by pipeline. More than one million miles of underground pipelines link natural gas fields to major cities across the United States.