Isothermal vapor-liquid equilibria (VLE) for the ethylene + 4-methyl-1-pentene and l-butene + l-hexene binary systems were measured by the static method at several temperatures for pressures in the range (0.3 to 8.5) MPa. Representations of VLE data by the Soave and Peng-Robinson cubic equations of state are compared in both modes : predictive and binary parameter adjustment. As the two binary systems behave almost ideally, there is no significant difference between their representation qualities through both equations of state.