The oxygen diffusion coefficient in a soda-lime-silica glass melt was measured by the EMF method with Pt and zirconia electrodes. The atmosphere was changed from air to N2 and then back to air, and the resulting EMF changes were monitored. In addition, oxygen diffusion profiles were numerically simulated and compared with experimental curves. The lead of the Pt electrode must be covered with insulating material to measure the penetration of oxygen in the melt from the surface. When silica was used as the insulator, the curve of EMF change showed relatively good agreement with the simulated curve. On the other hand, when alumina was used, a much more rapid EMF change was observed and the experimental and simulated curves did not agree.