Four comprehensive isotherm expressions are proposed for various water vapor adsorption mechanisms. Water vapor adsorption in micropores and on macropore walls is described using the Langmuir and Freundlich models, respectively. Water vapor condensation in the pore core volume of macropores is modeled by assuming that the effective pore size follows a Gaussian and uniform distribution. These expressions are used to fit water adsorption data on various kinds of alumina. The results show that the proposed water vapor adsorption isotherm expressions fit the water adsorption data well. (c) 2013 Elsevier B.V. All rights reserved.