The performance of a cocurrent downflow contactor (CDC) bubble column reactor has been examined using a first order reaction involving the palladium catalyzed hydrogenation of itaconic acid. The reaction was carried out at ambient temperature and in the pressure range 110-290 kPa using 5% and 10% w/w Pd/charcoal catalysts in two solvents (water and 2-propanol). The quantitative evaluation of the mass transfer and kinetic parameters was achieved using the classical film model for a first-order reaction. Because of the large specfic gas-liquid interfacial area generated in the CDC, k(L)a, the volumetric gas-liquid mass transfer coefficient was large (0.4-6 s(-1)) and was comparable with that of a much smaller stirred reactor (similar to 1/10 in size) with only similar to 10% of the latter’s energy consumption. Unlike conventional bubble columns where the gas-liquid mass transfer is often the rate limiting step for this type of reaction the relative contribution of the gas-liquid mass transfer resistance in the CDC was low (1-50% of the total resistance) compared with the liquid-solid mass transfer and surface reaction resistances for the three-phase catalytic hydrogenation of itaconic acid. The liquid-solid mass transfer coefficient (k(s)) and first-order reaction rate constant (k(l)) in the CDC were similar to those obtained in the stirred reactor with both the liquid-solid mass transfer and surface reaction being important rate steps. However, the magnitude of k(s) and k(l) depends critically on the method of calculating k(s) and an independent evaluation of k(s) should be carried out to obtain more accurate k(l) values. These initial studies indicate that the CDC has good potential as a three phase catalytic reactor and unlike some bubble columns can be used for relatively fast reactions.