Abstract The development of advanced bioreactor systems for the processing of coal should follow some basic principles. Continuous operation is preferred, with maximum bioreagent concentrations and enhanced mass transfer. Although conventional stirred-tank bioreactors will be more appropriate for some processing concepts, columnar reactors with retained bioreagents could be the system of choice for most of the applications. The latter will include both stationary- and fluidized-bed configurations. The various characteristics of these systems are discussed in the context of bioprocessing of coal.