A theoretical and experimental study was conducted to accurately determine the amount of adsorption and desorption of methane by various Granular Activated Carbon (GAC) under different physical conditions. To carry out the experiments, the volumetric method was used up to 500 psia at constant temperature of 25 ℃. In these experiments, adsorption as well as desorption capacities of four different GAC in the adsorption of methane, the major constituent of natural gas, at various equilibrium pressures and a constant temperature were studied. Also, various adsorption isotherm models were used to model the experimental data collected from the experiments. The accuracy of the results obtained from the adsorption isotherm models was compared and the values for the regressed parameters were reported. The results shows that the physical characteristics of activated carbons such as BET surface area, micropore volume, packing density, and pore size distribution play an important role in the amount of methane to be adsorbed and desorbed.