In physics and thermodynamics, the Redlich–Kwong equation of state is an empirical, algebraic equation that relates temperature, pressure, and volume of gases.  It is generally more accurate than the van der Waals equation and the ideal gas equation at temperatures above the critical temperature.  It was formulated by Otto Redlich and Joseph Neng Shun Kwong in 1949.  It showed that a two-parameter, cubic equation of state could well reflect reality in many situations, standing alongside the much more complicated Beattie–Bridgeman model and Benedict–Webb–Rubin equation that were used at the time.  The Redlich–Kwong equation has undergone many revisions and modifications, in order to improve its accuracy in terms of predicting gas-phase properties of more compounds, as well as in better simulating conditions at lower temperatures, including vapor–liquid equilibria.