Adsorption isotherms for supercritical fluids are calculated using lattice theory. Results are compared with experimental data for methane on graphon and for carbon dioxide on coal, It is shown that the model reflects the peculiar features in adsorption isotherms of supercritical fluids (in particular, a maximum in the adsorption with increasing pressure), The analysis shows that there is two layer adsorption over a wide range of densities.