CO2 and CH4 equilibrium adsorption are predicted by Excess Gibbs energy models based on vacancy solution theory, for single and binary mixture on Multi-Walled Carbon Nanotubes (MWCNTs) functioned by NH2 group. The experimental data of single gas adsorption isotherms were obtained at moderate pressures and temperatures using the volumetric method in a static gaseous set up. Firstly, the equilibrium pressures related to the adsorbed amounts, for single gases, were correlated on Wilson and FloryHuggins activity coefficient equations based on vacancy solution theory and the model parameters were determined by fitting the model on the experimental data. Secondly, the pure component parameters were implemented in extended Wilson and FloryHuggins equations for CO2 and CH4 mixture to predict the gassolid phase equilibria. The results showed fairly good agreement between the experiments and both Gibbs models. Finally, the studied models were compared with the popular model of Extended Langmuir. The results revealed more accurately and precisely prediction of Wilson and FloryHuggins against Langmuir model for mixed gas of CO2 and CH4 on MWCNTNH2. (C) 2011 Canadian Society for Chemical Engineering