The goal of the US Department of Energy (DOE) Underground Coal Conversion Program is to develop technology to produce clean fuels from coal deposits that are unsuitable for commercial mining. DOE's strategy is to remove the high-risk elements of UCG by resolving technical, environmental, and economic uncertainties. This will enable industry to assume responsibility for commercialization of the technology. Thus, the elements of the program have been designed to: provide detailed design and operational data that industry can use to scale-up with confidence; provide accurate and complete cost estimates that will allow comparison between alternative processes; provide detailed environmental impact and control data to allow industry to implement projects that will meet applicable standards; verify the reliability of continuous operation of UCG processes; and show that UCG processes have the flexibility to meet a variety of commercial needs. The Underground Coal Conversion Program has successfully demonstrated the technical feasibility of UCG for subbituminous coals through a series of 13 federally sponsored UCG field tests. These tests have demonstrated both air and steam-oxygen injection, reverse combustion and directional borehole drilling to link process wells, and continuous operation for sufficiently long time periods (30 to 60 days) at high enough gasification rates (30 to 100 tons per day) to provide a good technical data base. A number of mathematical models have been developed and compared with field results to provide predictive capability. The need for extensive pre-operational site characterization has been demonstrated. 72 references, 5 figures.