C-13 high-pressure CPMAS NMR is applied to examine the interaction between a CO2 gas and polystyrene under CO2 gas pressures of 0-7 MPa. The molecular motion of polystyrene at atmospheric pressure is also studied for comparison by C-13 CPMAS NMR in the temperature range 35-104 degrees C. The obtained C-13 CPMAS MMR spectra and C-13 T*(1 rho) values show that while the interchain distances in the densely packing regions are heterogeneously expanded with increasing temperature, they are homogeneously expanded at high CO2 gas pressures.