In many studies involving a liquid and air, the effective permeability of the wetting phase (kw) is determined from the capillary pressure (Pc)--saturation (S) relation and a corresponding, measured kw value. The movement, and therefore the effective permeability, knw, of air in an air-liquid system is often ignored, especially by those who consider only the flow of water in soils. However, if a wetting and a nonwetting liquid coexist (two immiscible liquids), the effective permeability function of the nonwetting liquid must be determined as well. Rather than using some indirect method to determine the knw(Pc) or knw(S) relationship of the nonwetting liquid, we propose a direct measurement technique by using a permeameter which allows for steady state flow of the nonwetting liquid over a range of Pc and S values. During each steady state flow condition of the nonwetting liquid, Pc and S are constant and uniform throughout the permeameter, while the wetting liquid is at rest. The nonwetting liquid can either be a dense non--aqueous phase liquid (DNAPL) or a light non--aqueous phase liquid (LNAPL). The knw values are calculated as a function of Pc and S from the measured flow rates and the density difference between the wetting and nonwetting liquid. The proposed technique can be applied during drainage as well as imbibition. The S values are determined by recording the amount of water being displaced from the cell each time the Pc is changed. Results are discussed for the DNAPL perchloroethylene (PCE) and the LNAPL Soltrol. ¿ 1998 American Geophysical Union