The oxidation of glucose in the presence of glucose oxidase and catalase was employed for studying the oxygen transfer enhancement in an aqueous solution by additions of both n-hexadecane and soybean oil. Like surface-active agents, antifoam agents can decrease the oxygen transfer rate dramatically and thus played an important role in the oxygen transfer process. In the absence of antifoam agents, addition of n-hexadecane or soybean oil to the reaction medium caused decreases in the oxygen transfer rate (OTR). The extent of decrease was greater in soybean oil than in n-hexadecane. The spreading coefficient of the oil on water was found to be adequate for explaining this phenomenon. If the antifoam agent KM-70 was added to the reaction medium, however, an increased OTR could be obtained with addition of n-hexadecane or soybean oil. The enhancement in OTR was thought to be due to the removal of the antifoam-agent molecules away from the air-water interface by the oil added. The enzyme kinetics was verified to be unaffected by additions of KM-70, n-hexadecane and/or soybean oil. The present enzyme system is therefore adequate as a model for studying oxygen-vectors.