The distribution coefficients of benzene between slit pores and supercritical carbon dioxide at infinite dilution are calculated by the Monte Carlo simulation method over a wide temperature range. The Lennard-Jones potential function is used for describing interactions between benzene, CO2, and graphitic carbon. The distribution coefficient, K-2, which is defined as the ratio of the concentration of benzene in a pore to that in the fluid phase, is calculated from the residual chemical potentials of benzene, mu(2)(res), for both phases by applying Widom’s test particle insertion method. Under the condition of the constant fluid density, the logarithm of K-2 increases linearly with increasing reciprocal temperature, while it shows a maximum in the constant pressure condition. We observed a remarkable difference between the influence of density on mu(2)(res) : that is, mu(2)(res) in the fluid phase gets stabilized with an increase in fluid density due to the increase of number of CO2 molecules interacting with the benzene molecule, while mu(2)(res) in the pore becomes unstable with an increase in pore-phase density after the first monolayer near the wall has been occupied by CO2 molecules. The radial distribution functions of CO2 surrounding a benzene molecule in several pores of different slitwidths are displayed in three-dimensional graphics and they indicate how the benzene molecule and the surface walls influence the microstructure of CO2 in pores.