The paper discusses the possibilities of transformations of naphthenes in petroleum fractions (mainly motor fuels fractions) to keep or even improve their properties after saturating the present aromatics. Hydrogenolysis and ring-opening are the key techniques to achieve this goal. While higly-branched iso-alkanes are the targeted products in petrol, n-alkanes are desired in diesel fuel. A case study of a possible scenario to improve the quality of steam cracker feedstock is presented in detail.