A detailed experimental study of the adsorption behavior at equilibrium of pure nitrogen, methane, and carbon dioxide gases on a commercial carbon molecular sieve (Shirasagi MSC 3K-161) is reported at temperatures between 115 K to 323 K and pressures up to 5 MPa. A volumetric-type apparatus was used to obtain over 200 excess (Gibbs) adsorption capacity data over this range of pressure and temperature with an estimated uncertainty of 4 %. The absolute adsorption isotherms were type I in the IUPAC classification with the adsorption capacity at constant pressure increasing significantly with decreasing temperature. For each gas, the adsorption data were regressed to a four parameter Toth equation to represent the temperature and pressure dependence of the data with a relative standard uncertainty of 4 %. The optimized parameters from the Toth equation included the isosteric enthalpies of adsorption that were 17 kJ·mol⁻¹, 27 kJ·mol⁻¹, and 18 kJ·mol⁻¹ for N₂, CO₂, and CH₄, respectively.