Syngas fermentation for producing biofuels and other products suffers from mass transfer limitations due to low CO and H-2 solubility in liquid medium. Therefore, it is critical to characterize mass transfer rates of these gases to guide bioreactor design and optimization. This work presents a novel technique to measure the volumetric mass transfer coefficients (kia) for H-2 and CO using gas chromatography in a non-porous hollow fiber reactor (HFR). The largest measured kia for H-2 and CO were 840 and 420 h(-1), respectively. A model was developed to predict kia for H-2 and CO that agreed well with experimental data. This study is the first to measure, compare, and model both H-2 and CO mass transfer coefficients in an HFR. Based on model predictions, HFRs have the potential to be a reactor of choice for syngas fermentation as a result of high mass transfer that can support high cell densities.