Petroleum is the cheapest but not the only possible source of liquid fuels in this country. Petroleum substitutes can be obtained from tar sands, large beds of which are to be found in the West and in western Canada, and by extraction from coal and from oil shale deposits, which are extensive in Colorado and other Rocky Mountain states. Shale deposits in this country are said to contain at least 500 billion bbl of shale oil. Many of these deposits contain from 20 to 150 gal of oil per ton of shale.
Processes are available to recover the oil from the shale but at a cost today which generally speaking is higher than the cost of producing petroleum from wells. Coal, which is almost pure carbon, can be changed to liquid fuels by combining it chemically with hydrogen. This process today is also more costly than the production of these fuels from petroleum. Shale oil recovery and hydrogenation of coal are now economical in some European countries which are located far from crude-oil supplies in the ground. Thus, a shortage of liquid fuels, lubricants, and other products now derived from petroleum is hardly to be expected in this country for many generations.
