For the reliable design of crude oil and residua fractionators and fired heaters, accurate calculation method for vapor-liquid equilibrium (VLE), thermodynamic and physical properties is necessary. Recent trends using increasingly heavier crude oils, extracting the maximum light oils by deep-cut vaporization at high temperatures and high vacuum, and the decreasing demand for black oil products prompted this investigation. However, the accuracies of these methods in the calculation of vapor-liquid equilibrium of crude oils and their residues at high temperatures have not been thoroughly investigated and published by previous investigators. The purpose of this paper is to evaluate the accuracy of the currently available and often-used methods, and to investigate a new method for the VLE of high-boiling petroleum fractions. For this purpose, the equilibrium flash vaporization data (EFV) of four crude oils and their vacuum residues were used, which have been published by major oil companies. (C) 2010 Elsevier B.V. All rights reserved.