Petroleum diesel, which is also called petrodiesel or fossil diesel, is produced from the fractional distillation of crude oil (petroleum) at atmospheric pressure, within a temperature range of 200°C to 350°C. This results in a mixture of hydrocarbon chains that contains around 8 to 21 carbon atoms per molecule. The viscosity and the boiling point of the fuel increase with an increase in the number of carbon atoms. This helps in the separation of the various components by distillation.
The chains from C7 to C11 vaporize at temperatures below the boiling point of water and are used as gasoline. The products from the range of C12 to C15 form kerosene, diesel oil and heavier fuel oils. The No. 2 fuel oil is known as diesel oil and is used for running cars, trucks and other vehicles. The lubricating oils follow, ranging from very light to very thick motor oils, gear oils and semi-solid greases. Vaseline also falls in this category. Hydrocarbon chains above the range of C20 form solids, like paraffin wax, tar and asphalted bitumen.