A distinction is made between synthetic petrol, which is produced from coal and other raw materials by chemical processes, and natural petrol, most of which are obtained as a substance already present in petroleum denotes a mixture of liquid, volatile hydrocarbons or to be more precise, a mixture of alkenes, naphthenic and aromatic compounds with boiling points between 40° and 180°C.

Hydrocarbons is a general designation for chemical compounds which consist solely of the elements hydrogen and carbon and which readily burn to produce carbon dioxide and water if they are mixed with a sufficient quantity of air and then ignited. Petrol for use as a fuel for internal combustion engines is produced by following process:

The petroleum is pumped from the well though pipelines to storage tanks at the port of shipment, where the crude oil undergoes a preliminary purification treatments. Tankers convey the crude oil to other ports, where it is discharged into storage. From here it is distributed to the refineries e.g. through pipelines.

At the refinery the petroleum is preheated in heat exchanges, and then passed to the tube stills, where heated to a high temperature in special steel tubes. These stills are fired with oil which is likewise obtained from the crude oil. The crude oil, heated to a temperature of several hundred degrees, expands in the distilling column, where it is separated into fractions: power gas, light petrol and petrol.

The remaining of the original quantity is again passed through the still, is reheated to a high temperature, and is passed to a distilling column in which a vacuum is applied; because the distillation temperature can be kept considerable lower when the vacuum is employed. In this second column 20% of the original quantity of crude oil is split into petrol, 15% into fuel oils and 20% of the original oil. The residue, about 27% provides tar, pitch and coke or undergoes for processing whereby in some cases, more petrol is produced.

However, such petrol is more properly to be regarded as synthetic petrol. The various petrol factions are mixed and refined : the composition of the mixture depends on the time of year, in the winter the proportion of liquid petrol in the mixture is higher than in the summer.

Refinement involves various processing treatments whereby the quality of compounds, anti-knock agents, anti-oxidants etc. the result must be volatile fuel which must, among other properties, have a minimum octane number of 80 to 90, ignites easily does not gasify at room temperature, does not develop gumming, does not smell objectionably, and burns without residue. Such a mixture of substances is of extremely complex composition comprising two hundred individual constituents.