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Vapor-liquid equilibrium data for aqueous solutions of volatile weak electrolytes are needed in designing separation equipment in the chemical and oil-related industries. Because of chemical reactions between the weak base ammonia and sour gases like carbon dioxide and hydrogen sulfide, modeling of phase equilibria in such mixtures requires a lot of experimental information which is rarely found in the literature. Thus, it is not surprising that published correlations are often considered unreliable. More and better experimental material is essential to overcome this situation. Therefore vapor-liquid equilibrium in the ternary system ammonia-carbon dioxide-water was investigated experimentally in the temperature range between 333.15 and 393.15 K at pressures up tc about 7 MPa. The investigated concentration range covers water-rich mixtures to about 16 molal for ammonia and 13 molal for carbon dioxide. Altogether 559 data points are reported. In the region where both investigations overlap, the new experimental results are in good agreement with data reported by Miiller et al. (1988). For comparison with existing correlations the method by Edwards et al. (1978) with recently published parameters (Kawazuisbi and Prausnitz, 1987) is used. Predicted data agree well with the experimental results at low solute concentrations, but large deviations are observed near the minimum of the total pressure curve (in a plot vs. the concentration of carbon dioxide at constant concentrations of ammonia) and at very high solute molalities.