To understand capturing and/or enhanced gaseous selectivity of industrial flue gases containing CO2 and SO2 using room-temperature tonic liquids, we have developed a ternary equation of state (EOS) model for a CO2/SO2/l-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim]Tf2N]) system. The present model is based on a generic RK (Redlich-Kwong) EOS, with empirical binary interaction present model is based oil a generic RK (Redlich-Kwong) EOS, with empirical binary interaction parameters of each binary system. These interaction parameters have been determined using our measured VLE (vapor-liquid-equilibrium) data for SO2/[hmim][Tf2N] and CO2/[hmim][Tf2N] and literature data for CO2/SO2, The validity or the present EOS has been checked by conducting ternary VLE experiments for the present system. With this EOS, isothermal ternary phase diagrams gild solubility (VLE) behaviors have been calculated for various (T, P, and feed compositions) conditions. For large and equimolar CO2/ SO2 mole ratios, the gaseous selectivity is nearly independent of the amount of the ionic liquid addition. However, for small CO2/SO2 mole ratios the addition of the ionic liquid significantly increases the selectivity. The strong absorption of CO2 and SO in this ionic liquid may be practical for the simultaneous capture of these acid gases.