Abstract The long term stabilities of several reference electrodes in contact with an acidic Na2SO4 melt at 1200 K were studied. These included the specific Na+ ion probes: Ag/Ag+ mullite or β-Al2O3 or fused-silica, and O2(Pt)/Na2OWO3/fused-silica, and the specific O2− ion probes: CaO- and Y2O3-stabilized zirconia. Corrosion attack of the electrolyte tubes led to drifts in the measured potentials. The Ag/Ag+ fused-silica and the Y2O3-stabilized zirconia electrodes were found to provide the best stabilities.