The PR equation of state (EOS), as a representative of cubic EOSs, is applied to correlate gas solubilities in molten polymers in this work. Two existing mixing rules, the conventional van der Waals one-fluid mixing rule with one adjustable parameter (vdW1) and that with two adjustable parameters (vdW2), are used to test the capability of the PR EOS. The results show that the vdW1 is not enough, while the vdW2 can give acceptable correlations. A new mixing rule proposed in our previous work, which has been proved to work well for correlating VLE of polymer solutions using cubic EOSs, is further modified here. The new proposed mixing rule with one adjustable parameter shows greatly improved correlations than the vdW1, and is comparable with the vdW2 which requires two adjustable parameters. For 17 systems tested, the total average absolute deviation of pressure for the new mixing rule is 10.0% against 47.8% for the vdW1, and 12.1% for the vdW2.