In this article, an overview of recent achievements in Monte Carlo molecular simulation of aqueous systems is presented. Semi-empirical two-body potential models introduced recently allow accurate representation of the pure water vapor-liquid equilibria, including the critical region. Furthermore, these models are used for the calculation of water-hydrocarbon low and high pressure phase equilibria. Efficient methodologies for the simulation of highly dense system(s) and systems of long, chain molecules are discussed. In all cases, simulation results are compared against experimental data. Limitations of approximate molecular models are discussed.