"Oily rocks" were discovered by western Amer­ican pioneers whose rock hearths caught fire and burned. In order to yield their oil, these sedimen­tary rocks, called oil shales, must be crushed, heated, and refined after they are mined. Because the mining and refinement of oil shales require the expenditure of a great deal of energy, it is not cost-efficient to process oil shales that do not yield a significant amount of oil. Large oil shale deposits are located in the United States, Russia, China, and Canada. Wyoming, Utah, and Colorado have the largest deposits in the United States. Like tar sands, oil shale reserves may con­tain half again as much fuel as world oil reserves.

    Gas hydrates are reserves of ice-encrusted nat­ural gas deep underground in porous rock. Deposits have been identified in the Arctic tundra, deep under the permafrost. It is possible that gas hydrates could be found in the deep ocean sediments of the continental slope, as well. The oil industry is not particularly interested in extracting gas from gas hydrates at present, because of the expense in­volved. In a pilot program in Siberia, Russian scien­tists have successfully removed natural gas from hydrate deposits by pumping methanol (an alco­hol) into the hydrate region. Natural gas that is associated with ice readily dissolves in methanol, which can then be pumped out of the ground.

    Most industries have the ability to switch fuels if one type becomes temporarily unavailable or too expensive. For example, most power utilities rou­tinely switch the type of fossil fuel they use. The automobile, however, is completely dependent on gasoline, which is refined from crude oil. The auto industry has been searching for a suitable liquid fuel that can be substituted for gasoline. Methanol (CH₃OH} and ethanol (CH₃, CH2OH) are alcohol fuels that may eventually replace gasoline. These synfuels can be produced from biomass—living plant or animal material. Metha­nol can also be produced from either natural gas (the least expensive source) or coal. One of the advantages of alcohol fuels is that they burn mote cleanly than gasoline. Although alcohol fuels produce CO₂ and therefore contribute to global warming, they produce substantially fewer nitro­gen oxides than gasoline does. Technological improvements in their production could bring their costs down, but currently they are not cost-compet­itive with fossil fuels.

Coal has also been used to produce a nonalcoholic liquid fuel. This process, called coal liquefaction, was first developed before World War II, but its expense prevented it from replacing gasoline production. Research in the 1980s resulted in a series of technological improve­ments that have lowered the cost of coal liquefac­tion, but it is still not cost-competitive. It may be­come commercially attractive when the cost of gasoline rises or when new innovations reduce the cost of producing liquid coal even further.

    Another synfuel is a gaseous product of coal. Coal gas has been produced since the 19th century. As a matter of fact, it was the major fuel used for lighting and heating in American homes until oil and natural gas replaced it in this century. Produc­tion of combustible gases (carbon monoxide and hydrogen) from coal is called coal gasification. A promising coal gasification technique was devel­oped at Stanford University, and since 1984, a pilot power plant that utilizes coal gas produced by the new technology has operated in southern Califor­nia.

    One advantage of coal gas over solid coal is that ii bums cleanly. Because sulfur is removed during coil gasification, no scrubbers are needed when coal gas is burned. Like other synfuels, coal gas is more expensive to produce than fossil fuels.

Environmental Impacts of Synfuels

Although synfuels are promising energy sources, they have many of the same undesirable effects as fossil fuels. Their combustion releases enormous quantities of CO2 into the atmosphere, thereby contributing to global warming. Some synfuels, such as coal gas, require large amounts of water dur­ing production and would therefore be of limited usefulness in arid areas, where water shortages are already commonplace. Also, mining the fossil fuels that are needed to produce synfuels damages the land. Enormously large areas of land would have to be strip mined in order to recover the fuel in tar sands and oil shales.