Present work deals with oxygen mass transfer in an oil-in-water biphasic medium, employed in the production of gamma-decalactone by the biotransformation of methyl ricinoleate. A bubble column contactor was used to carry out the absorption experiments. The influence of operating conditions (gas flow-rate and organic phase composition) upon the gas-liquid interfacial area and mass transfer coefficient has been analysed and experimental results allow describing the mechanism of oxygen transfer from gas phase into the biphasic medium. (C) 2009 Elsevier B.V. All rights reserved.