High-pressure vapour-liquid equilibria for binary and ternary high polar and asymmetric systems are calculated using the Peng-Robinson-Stryjek-Vera equation of state coupled with the Twu-Coon (TWMR), the Orbey-Sandler (OSMR) and the Wong-Sandler (WSMR) mixing rules. Modified UNIFAC model is used for determining the activity coefficient and excess Gibbs free energy. The calculated results are compared with the experimental data and good agreement is observed. The average absolute deviation percents (AAD%)s indicated that the WSMR has less AAD% than other mixing rules in most of cases.