Modeling of non-isothermal vapor-liquid equilibrium processes requires the availability of heat of vaporization data. An equation for calculation of heat of vaporization at normal boiling point has been developed which is particularly suited for pure hydrocarbons and petroleum fractions. The equation is simple to use and provides an improvement over the existing equations for pure hydrocarbons in wide boiling range. The equation is equally valid for crude oils, thus enabling the estimation of heats of vaporization needed for modeling of distillation units in oil refineries.