Phase equilibrium in binary mixtures of interest in wine and must distillation processes have been modelled using the Peng-Robinson equation of state. The mixing rules of Kwak and Mansoori and of Wong and Sandler were used. A new simple modification of the Regular Solution model for binary mixtures is also presented. The cases studied considered nine water+congener mixtures. The congeners included in the study are those regarded as legal compounds by the Chilean legislation for the production of a spirit made from grapes, called Pisco. The work allows concluding on the advantages, disadvantages and expected accuracy of the models used.