Adsorption is widely applied in separation and purification of gas mixtures and liquids. A competitive multicomponent multilayer kinetic Model is derived for adsorption on solid surfaces, without an artificial distinction between chemisorption and physisorption. The adsorption isotherm was derived based on the kinetic model. Molecular sizes and difference in interactions have both been considered in the model. Different adsorbate species can appear to have different saturation coverages when adsorbed onto the same given surface. The resulted isotherm has been shown to be able to describe binary adsorption experimental data. (c) 2015 Elsevier B.V. All rights reserved.