Several sets of mixing rules have been evaluated for use with the Trebble-Bishnoi-Salim equation of state (TBS EOS). Calculations for each rule have been performed on a screened Gas Processor’s Association (GPA) data base which contains 137 binary systems and spans very wide ranges of temperature and pressure. Classical quadratic mixing rules are compared to Schwartzentruber-Renon mixing rules and to a new mixing rule based on the previous work of Huron and Vidal, Schwartzentruber and Renon, and Wong and Sandler. The new mixing rule preserves the quadratic nature of the predicted second virial coefficient and forces excess volumes to be zero at infinite pressure. In order to satisfy both conditions it was necessary to include an additional a degrees/v parameter in the attractive parameter of the TBS EOS which results in a quartic equation in volume. The method of Huron and Vidal was used to incorporate a Margules excess energy model into the EOS at infinite pressure. Not surprisingly it was observed in the study that the more complex mixing rules are only of significant benefit in systems exhibiting large asymmetry or polarity effects. Classical mixing rules are shown to be adequate in most of the binaries investigated here.