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Syngas (mixture of CO, H₂ and CO₂) fermentation suffers from mass transfer limitation due to low solubility of CO and H₂ in the liquid medium. Therefore, it is critical to characterize the mass transfer in syngas fermentation reactors to guide in delivery of syngas to the microorganisms. The objective of this study is to measure and predict the overall volumetric mass transfer coefficient, <i>k</i>_L<i>a</i> for O₂ at various operating conditions in a 7-L sparged and non-sparged continuous stirred-tank reactor (CSTR). Measurements indicated that the <i>k</i>_L<i>a</i> for O₂ increased with an increase in air flow rate and agitation speed. However, <i>k</i>_L<i>a</i> for O₂ decreased with the increase in the headspace pressure. The highest <i>k</i>_L<i>a</i> for O₂ with air sparged in the CSTR was 116 h^&#8722;1 at 600 sccm, 900 rpm, 101 kPa, and 3 L working volume. Backmixing of the headspace N₂ in the sparged CSTR reduced the observed <i>k_La</i>. The mass transfer model predicted the <i>k</i>_L<i>a</i> for O₂ within 10% of the experimental values. The model was extended to predict the <i>k</i>_L<i>a</i> for syngas components CO, CO₂ and H₂, which will guide in selecting operating conditions that minimize power input to the bioreactor and maximize the syngas conversion efficiency.