Specific ATP concentration (SATP; g ATP g(-1) dry biomass) and specific oxygen uptake rate (SOUR) (mg O-2 g(-1) dry biomass h(-1)) have been employed to investigate biomass quality and activity, respectively, for Beneckea natriegens growing oil n-propanol under sterile conditions in a continuous stirred tank bioreactor (CSTB). Experiments have been performed in a 2-1 working volume CSTB at several dilution rates between 0.05-0.18 h(-1). ATP as extracted from culture samples using tris-EDTA boiling buffer and measured using the firefly luciferase assay. The SATP was found to increase from 0.43 to 0.85 mg ATP g(-1) dry biomass as the dilution rate increased from 0.05 to 0.18 h(-1). SOUR increased from 200 to 405 mg O-2 g(-1) dry biomass h(-1) over the same increase in dilution rate. A linens relationship was found between SATP and SOUR. A simple structured model in which the biomass is divided into an "active" and an "inert" compartment is used to describe this variation of SATP and SOUR with the dilution rare. The model has been verified using data obtained both in this work and in other work described in the literature.