In situ high-pressure ATR-IR spectroscopy was applied to simultaneously measure the sorption of CO2 in polyethylene glycol (PEG) with molecular weight 1500 and the polymer swelling. The band at ca. 2338 cm−1 corresponding to the antisymmetric stretching mode of CO2 was used to calculate concentration of CO2 dissolved in PEG while spectral bands of PEG at ca. 1100 cm−1 were used to calculate swelling of PEG as a function of temperature and pressure. This in situ approach allowed to observe CO2-induced melting of PEG and to assess intermolecular interactions between CO2 and polymer. The solubility of CO2 in PEG 1500 was influenced by both pressure and temperature. It remarkably increased with pressure until the CO2 critical value, then it approached a plateau. Higher solubility was observed at the lower temperature.