A new theoretical crossover model for the phase behavior of binary mixtures is presented that corresponds to the Leung-Griffiths model in the critical region and is transformed into the regular classical expansion far away from the critical point. The model is optimized to, and leads to good agreement with, experimental vapor-liquid equilibrium data for CO2 + n-butane, CO2 + propane, ethane + benzene, CO2 + methanol, and dilute aqueous solutions of NaCl in the extended critical region. Phase behavior of mixtures in the presence of chemical reaction and a possibility to incorporate this phenomenon into the model are also discussed. Published by Elsevier Science B.V.