Gasoline and propane have lower boiling points and are therefore more volatile than diesel fuel and industrial fuel oil. This means that they vaporize and rise to the top of the distillation tower at lower temperatures than the heavier fuels. Conversely, diesel fuel and industrial fuel oil have higher boiling points and are less volatile, meaning they require higher temperatures to vaporize. As a result, they are removed closer to the bottom of the distillation tower where temperatures are higher.
