We extend the SAFT-VR Mie equation of state to calculate adsorption isotherms by considering explicitly the residual energy due to the confinement effect. Assuming a square-well potential for the fluid solid interactions, the structure imposed by the fluid solid interface is calculated using two different approaches: an empirical expression proposed by Travalloni et al. (Chem. Eng. Sri. 65, 3088-3099, 2010), and a new theoretical expression derived by applying the mean value theorem. Adopting the SAFT-VR Mie (Lafitte et al. J. Chem: Phys., 139, 154504, 2013) equation of state to describe the fluid fluid interactions, and solving the phase equilibrium criteria, we calculate adsorption isotherms for light hydrocarbons adsorbed in a carbon molecular sieve and for carbon dioxide, nitrogen, and water adsorbed in a zeolite. Good results are obtained from the model using either approach.. Nonetheless, Nonetheless, the theoretical expression seems, to correlate better the experimental data than the empirical one, possibly implying that a more reliable way to describe the structure ensures a better description of the thermodynamic behavior.