With the purpose of accurately representing the phase equilibria of hydrocarbon reservoir fluids, water, and methanol, the revised modified Patel-Teja model (MPT2 model) has been extended to predict the vapour-liquid (VL) and vapour-liquid-liquid (VLL) equilibria of hydrocarbon/water/methanol systems. The prominent feature of the work presented in this paper is the prediction of VLE and VLLE data. The accuracy and reliability of the extended MPT2 model has been demonstrated by exten-sively testing against diverse experimental data on VLE and reservoir oil systems containing water and methanol. The ex-tended MPT2 model can be easily applied to production schemes of natural gases from hydrate formations, hydrocarbon flowlines, and processing units.