The invention concerns a fuel for diesel engines, with a sulphur content of less than 500 ppm containing in a major proportion at least one average distillate from a straight-run distilling cup of crude oil, with temperature ranges between 150 and 400.degree. C. and in a minor proportion a lubricating additive containing monocarboxylic and polycyclic acids. The said fuel is characterized in that it contains at least 20 ppm of the additive consisting of at least one monocarboxylic aliphatic hydrocarbon, saturated or unsaturated, of linear chain between 12 and 14 carbon atoms, and at least one polcyclic hydrocarbon compound, containing at least two cycles each formed of 5 to 6 atoms one of which at most is optionally a heteroatom such as nitrogen or oxygen and the other atoms are carbon atoms, these two cycles having further two carbon atoms in common, preferably vicinal, these said cycles being saturated or unsaturated, substituted or non-substituted by at least one single grouping selected among the carboxylic, amine carboxyl, ester and nitrile groupings, the fuel containing more than 60 ppm of additive when the said combination is tall oil.