Fossil fuels supply almost all of the world's energy and feedstock demand. Among the fossil fuels, coal is the oldest, most abundant, and widely available form of fossil fuel. Coal constitutes over 75% of the world's fossil fuel. Since the beginning of the industrial revolution, coal has been the backbone of the world energy system. Before the discovery of oil and gas, coal was used to generate town gas via gasification for lighting and heating purposes. During World War II, coal gasification technology was extensively used in Germany to produce oil substitutes. After World War II, oil replaced coal as the major source of energy, and the interest in coal gasification remained dormant until the recent rise in energy prices. Since 2000, several gasification plants have become operational, most of these plants are for the production of chemicals and only a handful of plants for power generation. Coal is among the cheapest fuel available. Figure 20.1 compares the historical and projected price of major energy sources in the United States . Projections of the Energy Information Administration (EIA) indicate that coal is likely to remain the cheapest fuel in the foreseeable future and will likely become cheaper as the price of other preferred energy sources rise. Based on the energy content in terms of price per Btu, electricity commands the highest premium, followed by oil and gas. This price differential is a key driver that determines the interest in coal and its conversion into other energy substitutes.