A new simple and explicit reduced temperature and reduced pressure function has been proposed in the present study for modifying Redlich Kwong equation of state (EoS) to calculate the density of carbon dioxide in the supercritical region. The average absolute error of the model was found to be 1.63 and 2.07% in the comparison with the literature and NIST density data respectively, which demonstrates superiority of the model over other EoSs. (C) 2013 Elsevier B.V. All rights reserved.