Sorption of CH4, N-2, O-2, and Ar in ZSM-5 with different SiO2/Al2O3 ratios was studied by volumetric measurements and grand canonical Monte Carlo simulation. Sorption capacity for all the gases studied was observed to decrease with in increase in the SiO2/Al2O3 ratio of ZSM-5. The sorption selectivity of CH4 over N-2 increases, whereas sorption selectivities of N-2 over O-2 and Ar decrease with an increase in the SiO2/Al2O3 ratio of ZSM-5. ZSM-5 with SiO2/Al2O3 of 900 showed higher selectivity for CH4 over N-2, whereas the SiO2/Al2O3 ratio of 25 showed higher N-2 selectivity over O-2 and Ar. The heats of adsorption for CH4 and N-2 decrease and that for O-2 and Ar remain unaffected with an increase in SiO2/Al2O3 ratio of ZSM-5. The values of Henry's constant were also calculated for CH4, N-2, O-2, and Ar for adsorption in ZSM-5 having varied SiO2/Al2O3 ratio. The experimental results were compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Simulation studies expectedly showed the proximity of N-2 molecules to the sites occupied by extraframework sodium cations.