The term oil shale is technically incorrect in that the rock to which it refers, marlstone, is neither oil nor shale. Instead, it is a material that contains an organic substance known as kerogene. When heated to a temperature of 900°F (480°C) or more, kerogene decomposes, forming a petroleum-like liquid and a combustible gas. Huge amounts of high-grade oil shale exist in the western United States. By some estimates, these reserves could meet the nation's fuel needs for about a century. Although the technology for tapping these reserves already exists, it is still too expensive to compete with conventional fossil fuels or other sources of energy now in use.
See also Alternative fuels