Under anaerobic, carbon limited conditions, celluloytic fermentative microorganisms face a metabolic choice with respect to the allocation of relatively scarce ATP : to invest it in cells or in hydrolytic enzymes. A model is proposed that defines an allocation parameter reflecting the fractional expenditure of ATP on cell synthesis relative to the total ATP available (gross ATP synthesized less maintenance). This parameter is then incorporated into an ATP-centered model of anaerobic cellulose fermentation based on the ethanol fermentation of yeast and the cellulase system of Trichoderma reesei. Results indicate that high processing rates are possible via a consolidated bioprocessing strategy, especially at high cellulase specific activities, and that cell/cellulase allocation represents an interesting system in which to study, and perhaps exploit, microbial evolution and metabolic control.