The initial accelerated aging ("burn-in") and the subsequent alternate-line-aging (ALA) characteristics of the operating voltages of ac plasma display panels were studied for MgO films deposited on dielectric glass substrates at 25°-350°C in a residual gas pressure of 10-6-10-7torr. To study the effects of the presence of oxygen during film deposition, the films were also deposited in 10-4-10-5torr of oxygen. Films deposited at 350°C showed significantly better aging characteristics than those deposited in 25°C. This observed dependence of the aging characteristics on the various parameters of the panel-fabrication process is explained in terms of a postulated effect of oxygen on the surface properties of MgO films and the changes in the surface properties of the MgO films (caused by changes in the surface stoichiometry) produced by ion bombardment during the discharge.