In this set of experiments a magnetic suspension balance (MSB) was employed to measure the apparent solubilities of N-2 and CO2 in polypropylene (PP) and ethene/ octene copolymer melts, while the swollen volume predicted by the Sanchez-Lacombe (SL) equation of state (EOS) was used to account for the buoyancy effect. The swollen volume of the polymer/gas mixture, as well as the gas solubilities for both PP and the ethene/octene copolymer, are discussed. It was observed that the branched molecular structure limited the molecular movement, and therefore the volume swelling of the polymer/gas mixture. In a similar context, the solubility of both N-2 and CO2 were less in the branched polymer (ethene/octene copolymer) than in the linear PP. (c) 2006 Wiley Periodicals, Inc.