where xi is mole fraction of component i and θ is a parameter such as Tc or Pc. However,since in this work we have studied n-alkane mixtures it was found that it is simpler (with same degree of accuracy)to calculate M for the mixture and to use it in Eqs.(8) to (11) for calculation of all input parameters needed for Eq.(7). This method can also be applied to mixtures which are mainly paraffinic but also contain non-paraffinic compounds.