Various types of external loop airlift contactors (ELALCs) were examined for their hydrodynamic and mass transfer behavior. The investigation covered a variety of design parameters including the length of connection tubes (L-c), height of riser and downcomer (L-h), and the airlift configurations while maintaining the ratio between downcomer and riser cross sectional area constant at 0.269. The results demonstrated that the behavior of the external loop airlift could be modified by adjusting the design and operating variables. In general, a faster liquid velocity led to a presence of lower gas holdup and gas-liquid mass transfer rate. Increasing L-c and L-h seemed to increase liquid velocity while decreasing the overall gas holdup and the overall volumetric mass transfer coefficient. Empirical correlations for the estimation of the system behavior were finally formulated. (C) 2011 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.