In order to investigate the swelling effect of coal induced by gas adsorption

based on the assumption that the surface energy change caused by gas adsorption is equal to the change in elastic energy of the coal

a theoretical model is developed to describe gas adsorption induced swelling. The formulas of adsorptive expansion stress and strain of coal are derived. The model also is tested by experimental results of gas adsorption induced coal swelling from three aspects

such as low pressure

medium pressure and high pressure. The results show that the model agrees well with experimental data of coal deformation induced by the gas adsorption. It is shown that the model is able to describe the differences in swelling behaviour with respect to gas species and at different levels of gas pressures. It is also shown that the volume of the adsorption gas can be ignored when the effects of gas pressure on coal deformation is considered.