A simple, accurate, and widely applicable semiempirical vapor-liquid equilibrium model is developed for the HCl-water system. The model is based on the modified Raoult's law. adjusted to include a function known as the "pseudo-vapor pressure." The resulting set of equations relate total pressure, liquid bulk (nonionized) composition.. vapor composition: and temperature. The parameters were fit to a wide range of data available in the literature (-10 to 200 degreesC. 0.0026S-66.1 atm, and 2-54.9 wt % HCl) that includes the supercritical region. The final equations are demonstrated to allow straightforward calculation of azeotropes and dew points.