A high-precision gas chromatograph was used in conjunction with a quadrupole mass spectrometer and an on-line computer to study the fractionation of carbon and oxygen isotopes in carbon dioxide on two solid adsorbents and on a variety of liquid phases. For adsorption studies the relative retention is reported as a function of temperature on Porapak Q and silica gel. On the former, α values are on the order of 1.0027 ± 0.0001 (standard deviation) for the carbon isotopes and 1.0011 ± 0.0002 for the oxygen species, while on silica gel the values are 1.0031 ±0.0004 and 1.0050 ± 0.0008, respectively. Differential thermodynamic data have been reported. Using diethanolamine and polyethylene imine columns in gas-liquid chromatography, greater fractionation was found. However, column bleed and decomposition of the liquid phase were serious problems.