Producing biofuels from gasified biomass (synthesis gas) via microbial fermentation is currently being pursued as one alternative in biofuels development. In synthesis gas fermentation, reducing equivalents from H-2 oxidation via hydrogenase is important towards directing more carbon towards product formation. In this work, kinetic studies of H-2 utilization via the Clostridium P11 hydrogenase enzyme were performed to determine the most appropriate model to predict hydrogenase activity as a function of H-2 partial pressure. An important aspect of this work included the proper analysis of electron acceptors used in the kinetic studies. The K-H2 model parameter governing the effect of H-2 partial pressure on activity was similar to 30 kPa (absolute), independent of the type and concentration of electron acceptor. The K-H2 value indicates that H-2 partial pressures typically associated with syngas fermentation will result in compromised efficiency of the hydrogenase activity. (C) 2013 Elsevier Ltd. All rights reserved.