The extension of the ZLC isotherm measurement technique to the measurement of binary adsorption equilibria has been investigated experimentally. It is shown that, subject to certain obvious limitations, reliable binary adsorption equilibrium data can be obtained from analysis of the binary ZLC desorption curves. Separation factors are measured as a function of loading and adsorbed-phase composition for (CO2C2H4)-C-_ and (CO2C3H8)-C-_ on several cationic adsorbents (NaLSX, NaX, CaX, and CaA). All systems show strong energetic heterogeneities, leading to separation factors that decrease with loading. The experimental binary data for NaLSX are in good agreement with reported equilibrium data for these systems measured by conventional methods, thus providing direct experimental support for the new technique.