At low temperature near the normal boiling point, computer simulations of adsorption of gases can be compared directly with experiment. However, for adsorptive gas separations in which the gas is adsorbed near or above its critical temperature, absolute simulation variables must be converted to excess variables for comparison with experiment. The conversion of absolute to excess variables requires the helium pore volume of the adsorbent. Lennard-Jones potential parameters for helium gas molecules interacting with the oxygen atoms of silicalite are ε/k = 28.0 K and σ = 2.952 Å. The helium pore volume of silicalite is 0.175 cm3/g. Lennard-Jones potential parameters derived for Ar-O interactions in silicalite are ε/k = 93.0 K and σ = 3.335 Å. Density profiles for adsorption of argon in silicalite at 300 K show that the local density is highest in the middle of the channels where the gas-solid potentials overlap.