In the oil refining industry, the so-called fuel oil refers to an oil product specially used as fuel for various industrial combustion equipment (including boilers, etc.). ), excluding gasoline and light diesel oil. There are many kinds of fuel oil, some of which have very low viscosity and some are quite thick, but for most of them, they are basically heavy fuels with relatively thick viscosity. The main raw material for producing this kind of heavy fuel oil is the residual oil left after atmospheric and vacuum distillation of crude oil. According to the purpose, it can be divided into two categories: marine internal combustion engine fuel oil and furnace fuel oil. Refined oil refers to gasoline and diesel oil. The difference can be said to be in the order of use and refining.

Generally speaking, in the process of crude oil processing, the lighter components are always separated first. As a part of refined oil, fuel oil is a heavy residue product separated from crude oil after gasoline, coal and diesel oil in the process of petroleum processing. Therefore, it is called heavy oil and residual oil. It is mainly composed of petroleum pyrolysis residue and straight-run residue. It is characterized by dark brown viscous flammable liquid with moderate viscosity, good fuel performance and high calorific value, and contains more non-hydrocarbon compounds, gum and asphaltene. (Simply put, gasoline and diesel are refined from crude oil first, and then from fuel oil.)

Gasoline diesel oil is contained in crude oil (commonly known as petroleum).