A mathematical model of microbial kinetics was introduced to predict the overall volumetric gas-liquid mass transfer coefficient (k(L)a) of carbon monoxide (CO) in a batch cultivation system. The cell concentration (X), acetate concentration (C-ace), headspace gas (N-co and N-co2), dissolved CO concentration in the fermentation medium (C-co), and mass transfer rate (R) were simulated using a variety of kLa values. The simulated results showed excellent agreement with the experimental data for a k(L)a of 13/hr. The C-co values decreased with increase in cultivation times, whereas the maximum mass transfer rate was achieved at the mid-log phase due to vigorous microbial CO consumption rate higher than R. The model suggested in this study may be applied to a variety of microbial systems involving gaseous substrates. (C) 2017 Elsevier Ltd. All rights reserved.