The paper presents a useful method for investigating the flow path of the injected air, estimating the radius of influence, and assisting the design of well spacing of sparging wells. The method applies both tracer and modeling approach. A field test using helium as a tracer was conducted on an air sparging pilot. A 3-dimensional, 3-phase compositional model was utilized to simulate the air sparging process at the pilot. The model was first calibrated with the tracer concentrations observed in the field test at various locations between the air sparging well and the soil vapor extraction well. The calibrated model was then used to predict the flow path of the injected air and to simulate the water saturation distributions in the aquifer. The steady-state water saturation distributions was found useful for estimating the radius of influence of air sparging and for designing the well spacing of sparging well.