Change in the glass transition temperature, T-g, of poly(2,6-dimethyl phenylene oxide), PPO, due to the dissolved CO2 has been measured as a function of the gas pressure, p, using a high-pressure DSC cell. At 61.2 atm, the highest pressure studied, T-g is depressed by 31.6 degrees C. The depression in T-g is found to be linear with pressure, with dT(g)/dp of -0.5 degrees C atm(-1). The experimental results are in fair agreement with those calculated from a quasilattice solid-solution model for polymer-diluent systems. The present results, however, differ markedly from a recent investigation on PPO-CO2 system which reported a depression in T-g of 226 degrees C at 60 atm and a dT(g)/dp of -3.8 degrees C atm(-1).