This paper presents an experimental investigation of adsorption equilibrium characteristics of natural gas onto granular activated carbon (GAC). Experiments have been conducted at adsorption temperatures ranging from 20 degrees C to 50 degrees C and pressures up to 10 bar. The measurements are based on measuring the adsorption uptake difference between two equilibrium adsorption states. Experimental data have been correlated using four adsorption isotherm models, namely, Langmuir, Toth, Dubinin-Astakhov (D-A), with and without volume correction. The proposed method reduces the time required to conduct the experiments significantly. It is found that 1 kg of GAC can adsorb about 77 g of natural gas at adsorption temperature of 20 degrees C and equilibrium pressure of 10 bar. Isosteric heat of adsorption of natural gas/GAC pair has been estimated using Clausius-Clapeyron equation. Comparison between storage capacities of adsorbed natural gas and compressed natural gas has also been discussed. Results extracted from the present study are useful for developing efficient adsorbed natural gas storage systems.