A magnetic suspension balance was employed in experiments to measure gas solubility in the polymer melts. The gas solubilities of CO2 and N-2 in both linear and branched Polypropylene (PP) were investigated. The swollen volumes predicted by the Sanchez-Lacombe equation of state (EOS) and Simha-Somcynsky EOS were applied to incorporate the buoyancy effect, which is essential for the accurate measurement of solubility data. The effects of the branched structure on the swollen volume and gas solubility were discussed. It was observed that the long chain branched PP exhibited less expandability than the linear PP, due to the entangled molecular chain structure. Therefore, the total amount of gas that was able to dissolve into the long chain branched PP turned out to be less. (c) 2007 Wiley Periodicals, Inc.