Experimental data and theoretical predictions of hydrolysis reaction kinetics of model halocarbons and phase equilibria of their associated neutralized salt reaction products are reported for a range of hydrothermal conditions. Specifically, the results of a study of hydrolysis and oxidation of methylene chloride (CH2Cl2) to produce CO2, H2O, and HCl as final mineralized products are presented. An analysis of hydrolysis kinetics and heat transfer was used to generate kinetic parameters for comparison with theoretical predictions based on a modified form of the Kirkwood solution model to show density dependent effects as a function of the dielectric strength of the reaction solvent medium. Phase equilibria data for the ternary NaCl-Na2SO4-H2O, system at 200 and 250 bar were measured and correlated. A modified form of the Anderko-Pitzer semi-empirical PVTxi model was used to predict equilibrium phase boundaries for the NaCl-H2O system at 210, 250, and 300 bar. Molecular simulation results for the NaCl-H2O binary was used to illustrate changes in the solvation power of water as a function of density. © 1998 Elsevier Science B.V. All rights reserved.