<jats:p> <jats:italic>Aerobacter cloacae</jats:italic> UW-C83 and <jats:italic>Escherichia coli</jats:italic> K-12 were grown under various anaerobic environments. Y <jats:sub> <jats:sc>atp</jats:sc> </jats:sub> values were calculated by determination of cell weights and analyses for fermentation products. These Y <jats:sub> <jats:sc>atp</jats:sc> </jats:sub> values are compared with others reported in the literature. Limitation of growth by factors other than adenosine triphosphate supply is discussed.