Chromatographic experiments have been carried out with toluene and naphthalene in carbon dioxide to determine mass transfer coefficients in silica gel packed beds at 301-318 K, 54-150 atm, and 0.3 < Re < 7. Mass transfer coefficients are determined by direct matching of the chromatographic response curves in the time domain. The molecular diffusivities for toluene in CO2 are obtained from the Renkin equation and are reasonable. A generalized mass transfer correlation which considers both the effects of natural and forced convection and the effect of axial dispersion is developed at 0.3 < Re < 135 by using the experimental data and other literature data.