Quantitative representation of complicated behavior of fluid mixtures in the critical region by any of equation-of-state theories re-mains as a difficult thermodynamic topics to date. In the present work, a computational efforts were made for representing various types ofcritical loci of binary water with hydrocarbon systems showing Type Ⅱ and Type Ⅲ phase behavior by an elementary equation of state [calledmulti-fluid nonrandom lattice fluid EOS (MF-NLF EOS)] based on the lattice statistical mechanical theory. The model EOS requires two mo-lecular parameters which representing molecular size and interaction energy for a pure component end single adjustable interaction energyparameter for binary mixtures. Critical temperature and pressure data were used to obtain molecular size parameter and vapor pressure datawere used to obtain interaction energy parameter. The MF-NLF EOS model adapted in the present study correlated quantitatively well the criti-cal loci of various binary water with hydrocarbon systems.