The direct interaction between CO2 and two Argonne Premium Coals [Pocahontas No. 3 (low-volatile bituminous) and Beulah-Zap (lignite)] was probed by use of attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy at 328 K and pressures up to 8.0 MPa. Sorbed CO2 on Argonne Coals was detected at 2335 cm(-1) for Beulah-Zap coal and 2332 cm(-1) for Pocahontas No. 3 coal. The energy of adsorption (18.8-20.5 kJ/mol), estimated from the Langmuir equation, was consistent with physisorption. The spectral data indicated that only one type of site was available for sorption. No evidence could be found for specific interactions between CO2 and oxygen functional groups in the coals. The CO2-coal sorption isotherm was derived without estimating the CO2 compressibility and adsorbed layer density, both of which are needed in manometric techniques.