The steady state mass balance for dissolved oxygen in an undivided rotating cylinder electrode reactor was established. Cases involving the absence or presence of a diffusion controlled oxygen reduction reaction were treated. The results show that in the absence of the oxygen reduction reaction and under low electrolyte velocities employed industrially, the rotating cylinder electrode reactor, exhibiting a continuous stirred tank reactor behaviour, yields lower dissolved gas concentrations than a plug flow reactor. Therefore, the rotating cylinder electrode reactor leads to lower redissolution rates of the detached metallic particles by oxygen corrosion. The effect of the dissolved gas concentration in the inlet electrolyte also demonstrates the benefits of a prior degassing step in the flow sheet. The simpler equation derived in the absence of oxygen reduction may be used in its presence for inlet dissolved oxygen concentrations below saturation and industrially relevant electrolyte velocities ranging from approx. 0 to 0.3 m s-1 if metal deposition current efficiency is higher than 87% or, conversely, if the dissolved metal concentration to dissolved oxygen concentration ratio is greater than 27. An even simpler equation based on the added hypothesis of total desorption of the gas produced can also be used with electrolyte velocities below 0.025 m s-1. Finally, the derived equations allow optimization of the rotating cylinder electrode reactor.