Hydrocarbons constitute the most important fraction in any crude oil. Although their proportion in different crudes varies significantly (e.g. from 30–40% to 100% in gas condensates), they comprise up to 70 mass % in all petroleums on the average. The history of petroleum chemistry, as a scientific discipline, is in effect the history of the chemistry of hydrocarbons. Research in petroleum chemistry was initiated in the 1860’s by the well-known German chemist K. Shorlemmer, who discovered n-butane, n-pentane and n-hexane in crude oils from Pennsylvania (USA). Shorlemmer’s success was due largely to his prior involvement in the synthesis of normal alkanes, conducted in the laboratory of his mentor, A. Wtirz. The Russian chemist, V. V. Markovnikov, while studying local crude oils from the Baku region 20–25 years later, concluded that it is not aliphatic, but alicyclic hydrocarbons, i.e. saturated hydrocarbons of the cyclopentane and cyclohexane series, which he called naphthenes, that prevail in crudes. And again this discovery was aided by Markovnikov’s previous engagement in the synthesis and research of cycloalkane properties, undertaken in the laboratory of A. M. Butlerov. Thus, by the end of the 19th century, the methodological foundations for petroleum chemistry were already established, i.e. the synthesis of model hydrocarbons with their further identification in crudes. It was also then that original concepts on the chemical classification of oils emerged, suggesting their division into two main classes: paraffinic and naphthenic oils.