A new parametric crossover equation of state for pure fluids and binary mixtures, which incorporates the scaling laws asymptotically close to the critical point and is transformed into the regular classical expansion far away from the critical point, is proposed. A comparison is made with the experimental data for pure methane, ethane and n-butane, and for binary mixtures of methane and ethane, and of ethane and n-butane. The equation of state yields a satisfactory representation of the thermodynamic properly data in a large range of temperatures and densities. An application for dilute aqueous sodium chloride solutions is also discussed.