This paper describes a conceptual design of a coal-fired, fluidized-bed, combustor-based steam locomotive that was developed as an approach to displacing premium fuel (diesel). This approach draws on relatively mature technology and appears feasible for the near term. Guidelines for the conceptualization are based on two previous designs that are relatively contemporary, and were built and tested during the steam locomotive era. Conclusions of this conceptual design study are summarized as follows: (1) a total conversion from diesel locomotives to coal-fired steam locomotives would displace up to 280,000 barrels of oil per day; (2) a fluidized-bed, steam turbine locomotive has the potential to offer very significantly lower operating costs and environmental burdens than the diesel; (3) fuel operating costs per horsepower hour for three comparably sized systems are as follows: diesel - $.19, fluidized-bed combustion (FBC) condensing steam cycle - $.085, and the FBC noncondensing steam cycle - $.021; (4) a cost estimate to build one commercially proven (post-prototype) coal-fired, fluidized-bed locomotive unit is estimated at $3,400,000; (5) an environmental analysis indicates that effective SO/sub 2/ and NO/sub x/ control is readily attainable with the FBC approach. If industrial New Source Performance Standards (NSPS) are imposed, particulate emission is likely to be the most severe constraint to FBC rail applications; (6) in general, there are no insurmountable roadblocks to early commercialization of mobile FBC steam generators, based on this analysis; and (7) in addition, the development of an attractive, mobile FBC power system appears to have significant potential for marine applications and industrial steam generators, either for direct heating or cogeneration applications.