Monte Carlo simulation methods are combined for studying the adsorption equilibrium characteristics in supercritical fluids (SCF) : (i) the adsorption isotherms of adsorbate diluted in SCF and (ii) the distribution coefficient of adsorbate at infinite dilution. Carbon dioxide, benzene, and a slitpore of graphite plane walls are selected as a model system by use of the Lennard-Jones potential for representing interaction potentials. The calculated adsorption isotherms and the distribution coefficients have been interpreted by two factors : the solvent power of SCF and the competitive adsorptions in the adsorbed phase.