The lightest hydrocarbon distillates (from crude oil) are the most flammable, and volatile.
You’ve got (lightest to heaviest)
(1) Light Naptha - used in disposable lighters (NOT “ronson lighter fuel”) This is a compressed gas such as propane, butane, and/or pentane as liquid that vapourises as soon as you release the pressure. Puncture a throwaway lighter to see this in effect. Boils away quickly in air under no pressure. Can be lit by a spark. Contains C3H8 to C5H12
(2) Heavy Naptha - Pretty much the main constituent of Petroleum Spirit (Unleaded Petrol) Has a vapour that makes an exposive mixture in air at normal temperatures. Can be lt by a spark.
http://www.youtube.com/watch?v=QkJdaU92Ln8 Contains C4H10 to C12H26
Fuel Oils: Contains C10H22 to C20H42
(3) “Light” - Kerosines - Not as flammable as Petrol, but more flammable than Diesel. Used as Aircraft, Rocket, and Stove (paraffin) fuel. Cannot be set fire to with a match, unless atomized or wicked. Additives to keep the fuel from “freezing” will also make it more flammable (cut it with lighter fuels), thus it is easier to start a fire with “their” stocks of Kerosine aircraft fuel in a place like Norway than in this country.
A burning paraffin stove will have the same fumes as can be smelled near an airport…
(4) “Gas Oils” - What we call Diesel, DERV, cherry or clear. Has to be wicked or compressed to auto-burn. Stick a burning match into it, and it’ll go out. Can be set alight IF heated up first to create an over-vapour…
Chemically, they’re pretty much the same - with different coloured dyes added for taxation purposes.
(5) Heavy Fuel Oil - Can be used to run a boiler, but has to be pumped/atomized from cold. Viscosity too high to be used for engines.
C16 and upwards are effectively “wax”. Since fuel oils contain hyrdrocarbons in the range C10 to C20, it is possible to “wax” them at low temperatures. Those waxes that are already entirely solid at room temperature will of course contain only those heavier non-volatile hydrocarbons upwards from C16… These have to be MELTED, and wicked, to burn.