The Gibbs ensemble MC method has been used for computing adsorption equilibria for binary mixtures of butane and CO2 in a slitpore of width 2 nm at 344.3 K and two pressures, 6 and 10 MPa. The adsorption of butane from supercritical CO2 decreases with increasing pressure while the adsorption of CO2 increases with increasing pressure; the enhanced solubility in supercritical CO2 has been illustrated for the major reason of the adsorption decrease of butane. The local density profile and the radial distribution functions in a pore are shown for each component. Three-dimensional graphics is shown to be a powerful technique for representing the radial distribution functions to understand the molecular structure in a slitpore.