The diffusion of nitrogen. oxygen and argon gas through a porous platinum sample was experimentally investigated. Unlike nitrogen and argon gas the diffusion flow rate of oxygen gas shows a strong temperature dependence in the temperature range considered (300-1000 K). The diffusion flow rate of oxygen decreases with increasing sample temperature. The observed effect is explained by ozone formation and back diffusion which reduces the total oxygen mass (oxygen and ozone) diffusion Bow rate. Ozone is formed inside the porous platinum sample. (C) 1997 Elsevier Science Ltd.