In order to extend the applicability of a Peng-Robinson group contribution method called PRASOG to ammonia-containing systems, the group pair parameters were determined using binary vapor-liquid and vapor-liquid-liquid equilibrium data. The vapor-liquid and vapor-liquid-liquid equilibria were predicted using the determined parameters for the binary and ternary systems containing ammonia, paraffins, olefins, water, alcohols, and nitriles. The predictive accuracy of liquid-liquid equilibria using group pair parameters from liquid-liquid equilibrium data is compared with those using the parameters from vapor-liquid equilibrium data.