This article describes the solubility of carbon dioxide, ethylene and propane in 1-octene based polyethylene of 0.94, 0.92, 0.904, and 0.87 densities. The isotherms obtained in the gas sorption experimental device display a sorption behavior similar to that of glassy polymers. We apply the dual model to semicrystalline polymers assuming that Henry's sites are related to the amorphous phase, which decreases when the crystallinity percentage increases, whereas the surface of the crystalline phase acts as a Langmuir site with higher gas-polymer affinity than glassy polymers. The good concordance of the calculated k(D) values, using the Flory-Huggins theory of polymer diluent mixtures, with the experimental results suggest that Henry's gas sorption fulfills this theory and, therefore, it may be a suitable way to estimate polymer-gas enthalpic interactions. Particularly, the variation of kD with the crystallinity fraction is exponential and the proportionality of the total sorption with the amorphous content seems only apparent. (c) 2007 Wiley Periodicals, Inc.