Microbial fuel cells containingProteus vulgaris and oxidation-reduction (“redox”) mediators were investigated. The bacteria were chemically immobilized onto the surface of graphite felt electrodes, which supported production of continuous electric current and could be reused after storage A computer-controlled carbohydrate feed system enabled the cell to generate a constant output with improved efficiency compared to the performance obtained with single large additions of fuel. The response to additions of substrate when immobilized bacteria were used was faster than that achieved with freely suspended organisms. This is attributed to the advantageous mass-transfer kinetics resulting from the proximity of the immobilized bacteria and the electrode surface.