There are two broad categories of distillation which are atmospheric and vacuum distillation. Within these two categories there are three distillation methods: True Boiling Point distillation (TBP), ASTM distillation, and Equilibrium Flash Vaporization distillation (EFV). As the names imply, atmospheric distillation runs at atmospheric pressure while vacuum distillation runs lower than atmospheric pressure that allows very high boiling point compounds to boil at lower temperatures.

The first of the three distillation methods, TBP, distills the crude in a batch operation. As the crude is heated each component converts to vapor at its specific boiling point. The vapor is separated from the other liquids using what are known as theoretical plates of which there are more than 100 in the column. Another aspect of this method is that the products are stringently purified using a reflux technique which involves heating and cooling vaporized distillates while in the distillation unit or just outside the unit and put back in. By combining the high number of theoretical plates with a reflux ratio, meaning the ratio of amount of reflux to amount of products, this procedure provides the greatest purity of product of the three distillation types.

ASTM works similar process to TBP however it does not use the theoretical plates or have reflux (and therefore no reflux ratio). In the end this process looks much more like a typical distillation unit which heats a liquid to a boiling point and cools and collects the condensate. This process provides slightly lower quality products.

EFV is similar to ASTM however it heats a flowing feed of crude rather than heating a batch. Once heated the feed enters a flash drum where the crude that has boiled off to vapor will separate from the other liquids. This provides the lowest quality products of the three methods.