DISTILLATION IS THE MOST WIDELY USED SEPARAtion process in the petroleum industry. Knowledge of the boiling range of crude oils, refined fractions, and finished products has been an essential part of quality determination since the beginning of the refining industry. Routine laboratory scale physical distillation tests have been extensively used for determining the boiling ranges of crude feedstocks, distillation fractions, and a complete slate of refinery products (ASTM methods D86, D1160, D2892, and D5236) [1–4]. An alternative to physical distillation or true boiling point distillation is simulated distillation by gas chromatography. Eggerston et al. first described simulated distillation in 1960 [5]. Simulated distillation (SD) is equivalent to a 100 theoretical-plate physical distillation, is very rapid, reproducible, and easily automated, requires only a small microlitre sample volume, and can better define initial and final boiling points. Boiling range distribution data are used to evaluate new crude oils, to confirm crude quality, to monitor crude quality during transportation, and to provide information for the optimization of refinery processes. The ability to quickly and reliably evaluate crude oils and fractions has important economic implications. The full development of simulated distillation methods as routine procedures has had a significant impact on the ability to determine boiling point information for crude oils and petroleum products.