The adsorption separation process of diluted gas mixtures containing carbon dioxide and methane on activated carbon has been investigated. Experimental breakthrough curves for both the adsorption and desorption processes have been obtained using mixtures of one or two adsorbable components and one nonadsorbable. A parametric study was conducted to determine the influence of temperature, inlet partial pressure, and superficial velocity on the performance of the adsorption process. The separation factor for the activated carbon was determined to be 3-3.5 at 40 degrees C and 2.7-2.8 at 60 degrees C. The experimental curves have been calculated using a mathematical model based on the approximations of local equilibrium and isothermal conditions. The system of differential equations was solved numerically using a Crank-Nicolson finite difference discretization scheme. The resulting nonlinear system of equations was solved iteratively using the Gauss-Seidel method. The parameters in the model have been estimated either by empirical correlations or using experimental data. The model simulations for both the adsorption and desorption processes are generally in good agreement with experimental data. The evident deviations that resulted in a few cases can be attributed to deficiencies in the Langmuir model itself.