A dual-media multiphase flow approach is proposed for modeling the local interphase mass transfer that occurs during in situ air sparging. The method is applied to two- or three-phase flow in porous media to simulate the small gas channels that form during air sparging, allowing resolution of the local diffusive mass transfer of contaminants between the flowing gas phase and nearby stagnant liquid-filled zones. This approach provides a good match with laboratory column experiments in which dissolved trichloroethylene (TCE) is removed by air sparging, and it is shown that the simulation results are very sensitive to the nature of the local mass transfer regime. The numerical model is then applied to hypothetical field air-sparging cases involving either a dissolved plume of TCE or a TCE nonaqueous phase liquid source. In these simulations the local mass transfer appears to play a much smaller role than in the laboratory-scale tests, and significant deviations from local equilibrium simulations only occur when the mass transfer rates are reduced below the calibrated laboratory-scale values. ¿ 2000 American Geophysical Union