A recently developed model for the current efficiency in chlorate electrosynthesis assumes a linear axial increase of the hypochlorite bulk concentration in the electrochemical reactor. The model is intended to improve the model developed by Beck assuming constant concentration in the interelectrode gap. Since none of these model assumptions can be realistic, the true axial concentration profile was studied taking account of the interaction of current density and volume fraction of gas, of the resulting variation of flow velocity and of mass transfer of hypochlorite. It was found that the deviations of the real concentration profiles from the linear profile are small. The improved current efficiency equation turns out to be a useful engineering tool in predicting the effect of all relevant design parameters.