"The current price of petroleum and the possibility of foreign embargoes have prompted the United States to search for alternative sources of energy. Coal offers one possibility since the U.S. has some of the world 's largest deposits. Unfortunately, the majority of the known reserves in the U.S. are not economically recoverable at the present time. Therefore, the conversion of coal in place underground into combustible gases or feedstocks, termed underground coal gasification (UCG), promises to become an important method of coal utilization in the future. The U.S. coal resource that is suitable for UCG, and not currently suitable tor conventional mining methods, has been estimated at nearly 2 trillion tons (Draffin, 1979). UCG can be simply characterized as the partial oxidation of coal in place (in-situ) in the presence of gasifying agents such as air or oxygen and steam, and the withdrawal of the gaseous products through production wells. The linked vertical well process, one technique employed in UCG, is illustrated schematically in Figure 1. This process involves drilling two vertical wells into the desired coal seam a short distance apart (up to 30 meters) , enhancing the permeability of the coal seam between the two wells by reverse combustion or directional drilling, igniting the coal at the bottom of one well, injecting a large volume of air or oxygen and steam, and recovering the gaseous products through the other well."