The photoelectrochemical treatment of waste water using immobilised TiO2 electrodes has been demonstrated to be an attractive alternative to TiO2 slurry reactors; however, it is generally believed that the diffusion of species to the surface of the catalyst imposes severe mass transfer limitations and hence is a disadvantage of the photoelectrochemical approach. To challenge this view, this paper reports the characterization of the mass transport properties of a novel gas sparged photoelectrochemical reactor. It is shown that passing a constant stream of nitrogen gas through the reactor increased the mass transfer coefficient by an order of magnitude above that in the absence of gas and this was attributed to the turbulent flow regime imposed by rising gas bubbles. It is also demonstrated that the gas-liquid transfer coefficient was greater than that for the rate of liquid diffusion and this has important implications for heterogeneous processes.