Vitrain, clarain, and fusain lithotypes of Pennsylvanian age high volatile bituminous coal from the Springfield Coal Member of the Petersburg Formation and the Lower Block Coal Member of the Brazil Formation from Indiana were examined using standard and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) prior, during, and after exposure to CO2 to investigate any potential physical or chemical alterations of the coal lithotypes. These lithotypes were distinct petrographically (vitrinite content ranged from 94.0 to 11.6 vol %), as well as with regard to surface area, microporosity, mesoporosity, and Langmuir parameters (volumes and pressures). Specifically, BET surface area for the Springfield Coal ranged from 6.0 m(2)/g in fusain to 10.0 m(2)/g in vitrain and for the Lower Block Coal ranged from 15.9 m(2)/g in fusain to 115.4 m(2)/g in vitrain. For the Lower Block Coal, Langmuir volumes (on an as-received basis) were 51 cm(3)/g in vitrain, 37 cm(3)/g in clarain, and 34 cm(3)/g in fusain; for the Springfield Coal, 42 cm(3)/g in vitrain, 42 cm(3)/g in clarain, and 24 cm(3)/g in fusain. During experiments performed at 17 degrees C and CO2 pressure up to 4.1 MPa (600 psig), the only observed changes in the infrared spectra were due to sorption of CO2 reflected by bands at 2333 cm(-1) (with a shoulder at 2320 cm(-1)) and at 657 cm(-1). These absorption bands increased in intensity as CO2 pressure increased, but they disappeared after desorption of CO2 in flowing nitrogen, suggesting physical sorption of a reversible nature. Absorption bands characteristic of the lithotypes did not change during or after CO2 exposure. Comparing the CO2 sorption capacity among various lithotypes suggests that vitrains adsorb the most CO2 and fusains the least. Also varying amounts of time were needed to fill the available pore space; more time was needed to saturate vitrains with CO2 than the other lithotypes,