Edited sentence: 1 fuel oil, No.1 is similar to kerosene and is the fraction that boils off right after gasoline.2 diesel fuel oil are almost the same thing (diesel is different in that it also has a cetane number limit which describes the ignition quality of the fuel).2 distillate and No.2 fuel oil and No.2 fuel oil, No.3 fuel oil are  variously referred to as distillate fuel oils, diesel fuel oils, light fuel oils, gasoil or just distillate.Distillate fuel oils are distilled from crude oil.For example, No.Fuel oil is classified into six classes, numbered 1 through 6, according to its boiling point, composition and purpose.Gas oil refers to the process of distillation.Price usually decreases as the fuel number increases.The boiling point, ranging from 175 to 600 °C, and carbon chain length, 20 to 70  atoms, of the fuel increases with fuel oil number.The oil is heated, becomes a gas and then condenses.Viscosity also increases with number, and the heaviest oil has to be heated to get it to flow