Recently compressed carbon dioxide is brought in as a substitute for conventional solvents in the chemical industry. To meet economic and ecologic demands it is necessary to recycle the CO2 in a circuit and it is therefore necessary to remove undesired components (e.g. unconverted H-2 from hydrogenation reactions). This study deals with the purifying of carbon dioxide under high pressure by means of gas permeation. For the separation of H-2 from a CO2/H-2 gas mixture under high pressure a polyethylene terephthalate membrane is employed. The influence of temperature and feed gas pressure on the permeability coefficients and separation factors of carbon dioxide and hydrogen is reported. The investigations were made within a temperature range of 10 to 70 degrees C and a pressure up to 190 bar.