We have measured the solubility and diffusion coefficients of carbon dioxide in four polymer substrates at 313 K and 10.5 MPa. The polymer substrates included poly(chlorotrifluoroethylene!, cross-linked poly(dimethylsiloxane), poly(methylmethacrylate), and cross-linked polystyrene. Solubilities were determined from maximum mass gain measurements when a film of each polymer was contacted with carbon dioxide, and diffusion coefficients were determined from timed absorption experiments. The highest solubility and the highest diffusivity were obtained with poly(methylmethacrylate).