The National Aeronautics and Space Administration Lewis Research Center, under an agreement with the Bureau of Mines, performed an assessment of alternative power sources for mining applications, primarily mobile underground equipment. The alternative power sources were divided into two categories, heat engines and energy storage systems, because heat engines are basically limited by emissions and energy storage systems are limited by energy storage density. Each alternative power source is described briefly, including its current development status, specific problem areas, and possible future improvements. Each is then evaluated against the requirements initially established. Research and development efforts for each alternative power source are discussed and evaluated in terms of potential.