When a nickel cathode is used during electrolysis, the separation factor γ of D2O/T2O is measured and found to be 2. When a platinum cathode is used, the value of γ is found to also be 2. This value is the same as the value that was measured and reported in an earlier paper that dealt with the use of a palladium cathode. A mathematical model that predicts the tritium concentration in the electrolysis cell finds the predictions to be in agreement with the measured values of tritium concentration in the cell. Excess tritium concentration is observed in the recombined off-gases in the case of the nickel cathode.