New molecular models for Hydrazine and its two most important methylized derivatives (Monomethylhydrazine and Dimethylhydrazine) are proposed to study the fluid phase behavior of these hazardous compounds. A parameterization of the classical molecular interaction models is carried out by using quantum chemical calculations and subsequent fitting to experimental vapor pressure and saturated liquid density data. To validate the molecular models, vapor-liquid equilibria for the pure hydrazines and binary hydrazine mixtures with Water and Ammonia are calculated and compared with the available experimental data. In addition, the Henry's law constant for the physical solubility of Argon, Nitrogen and Carbon Monoxide in liquid Hydrazine. Monomethylhydrazine and Dimethylhydrazine is computed. In general, the simulation results are in very good agreement with the experimental data. (C) 2012 Elsevier B.V. All rights reserved.