The steady-state mass balance for dissolved oxygen in a divided rotating cylinder electrode reactor was established. Cases involving the absence or presence of hydrogen evolution, as in, respectively, copper and zinc deposition, were treated. The results show that the importance of the diffusion controlled oxygen reduction reaction on metal deposition current efficiency is considerably decreased at low electrolyte flow rates used industrially by separating the reactor with a membrane, thus preventing the oxygen formed at the anode from reaching the cathode. Further substantial gains are achieved if hydrogen evolution takes place in the reactor, allowing a very efficient desorption mechanism of dissolved oxygen, but the global effect on metal deposition current efficiency remains unfavorable. The influence of several parameters on dissolved oxygen concentration inside the reactor and metal deposition current efficiency, such as electrolyte how rate, mass transfer coefficient, current density and inlet electrolyte dissolved gases concentration (oxygen and hydrogen), is also discussed. Comparison with experimental data for copper and cadmium deposition show that the derived equations appear adequate, although more data is required to make a complete assessment. Finally, the derived equations allow optimization of the rotating cylinder electrode reactor.