The effect of the sparger structure on the hydrodynamics and mass transfer characteristics of an internal loop airlift reactor was investigated. Three spargers with different diameters and numbers of orifices were tested. Two different flow regimes, i.e., homogenous flow and heterogeneous flow, were identified within the experimental range of superficial gas velocities. It is found that the sparger structure has more significant effect on hydrodynamic parameters in the heterogeneous flow regime than in the homogenous flow regime. The largest gas holdup and downcomer liquid velocity were obtained with the 4-orifice nozzle, followed by the O-ring distributor and the 2-orifice nozzle. The sparger structure has less effect on the oxygen transfer coefficient k(L), while it strongly affects the specific interfacial area a. The 4-orifice nozzle improved the volumetric mass transfer efficiency for that it generated a smaller mean bubble diameter and therefore a larger specific interfacial area than other spargers. Based on the material conservation and pressure balance principles, a hydrodynamic model was established to predict the liquid velocity in the downcomer, as well as the liquid velocity and the cross sectional area of the up-flow in the riser. Empirical correlations were proposed for different spargers, which well predicted the gas holdup and the volumetric mass transfer coefficient. (C) 2011 Elsevier B.V. All rights reserved.