Chemically specific surface diffusion of oxygen was observed on a porous glass membrane modified on its pore surface with cobalt porphyrin (CoP) which binds oxygen specifically and reversibly from air. The membrane displayed both permselectivity for oxygen and high permeability. The enhanced and specific diffusion of oxygen was mathematically analyzed with a parallel model involving surface diffusion of oxygen via CoP fixed on the pore surface and gas phase or Knudsen diffusion. alpha(3) beta-CoP was characterized by larger rate constants of oxygen binding (k(on)) and oxygen dissociation (k(off)), gave a larger surface diffusion constant of oxygen (D-S similar to 10(-4) cm(2) s(-1)), and brought about higher oxygen permeability through the membrane.