The use of a Carberry-type reactor has been investigated for the complete oxidation by oxygen of various water-soluble organic compounds over a platinum on porous polydivinylbenzene catalyst. Studies with aqueous formaldehyde as the test reactant reveal important details of reactor hydrodynamics and possible reaction pathways. Two routes for the transfer of oxygen are apparent in this reaction system. At low stirrer speeds ( < 1000 rpm), dissolved oxygen is observed to play a significant role in the reaction, whereas at higher stirrer speeds, gas phase oxygen mass transfer is found to be primarily responsible for the oxidation reaction. In the latter case. the presence of a gas envelope at the surface of this highly hydrophobic solid catalyst appears to play a key role in the oxygen transfer mechanism. unlike the situation for oxidation over conventional, hydrophilic (wetted) solid catalysts. Reaction rate-stirrer power correlations show that the important factors controlling the reaction kinetics are gas-liquid interfacial area and resistance to gas phase reactant transfer into the catalyst bed. Although experiments with a number of different catalyst bed designs indicate that the use of an annular bed geometry significantly decreases the latter resistance, it is observed that interparticle (bed) mass transfer is dominant. even at the highest stirrer speed achievable. Apparent reaction orders for both gas phase oxygen (0.6) and formaldehyde (zero) are markedly different over this hydrophobic catalyst, compared with those reported by other workers for the same reaction over a hydrophilic catalyst. These differences are attributed to the presence of the aforementioned gas envelope at the catalyst surface.