This work describes a device designed to allow the rapid measurement of vapor/liquid equilibria, Including vapor pressure and solute activity coefficients, in an automated fashion based on a conventional gas chromatograph. Various correction factors needed to convert the analytical signal (peak area) to the desired thermodynamic quantities have been developed. In general, activity coefficients at low concentration (mole fraction less than 0.01) are in good agreement with literature values (ca. 2%). Similarly, vapor pressures can be measured with good accuracy. The precision of measurement is often better than 0.5%. The major limitation in the accuracy of the method appears to be the lack of high quality experimental gas phase virial coefficients.