The continuous description of enthalpies of vapors and liquids is a considerable problem for engineers working with commercial simulators. The specific heat capacities for ideal gas (c(p)(id)) and liquids (c(p)(liq)) as well as the specific enthalpy of vaporization Deltah(v) are essential for engineering calculations. Typically, in standard applications, the specific liquid heat capacity is calculated indirectly from correlations for c(p)(id) and Deltah(v) and an equation of state. These equations usually do not make use of experimental c(p)(liq) data. Therefore, the indirect calculation Of c(p)(liq) yields considerable errors. The paper shows that the bad results are not mainly caused by inaccuracies of the quantities that have contributions to c(p)(liq) but by an ambiguity of the correlation of the enthalpy of vaporization. The problem can be overcome by fitting cp and the enthalpy of vaporization simultaneously. The solution can easily be integrated into commercial process simulators without defining new correlation routes or correlations. It is possible to extend it to substances showing vapor-phase association.