The absorption of oxygen in aqueous-organic solvent emulsions was studied in a laboratory-scale bubble reactor at a constant gas flow rate. The organic and the gas phases were dispersed in the continuous aqueous phase. Volumetric mass transfer coefficients (k(L)a) of oxygen between air and water were measured experimentally using a dynamic method. It was assumed that the gas phase contacts preferentially the water phase. It was found that addition of silicone oils hinders oxygen mass transfer compared to air-water systems whereas the addition of decane, hexadecane and perfluorocarbon PFC40 has no significant influence. By and large, the results show that, for experimental conditions (organic liquid hold-up <= 10% and solubility ratio <= 10), the k(L)a values of oxygen determined in binary air-water systems can be used for multiphase (gas-liquid-liquid) reactor design with applications in environmental protection (water and air treatment processes). (c) 2006 Elsevier B.V. All rights reserved.