Fuel composition for internal combustion engines which comprises a larger portion of fuel and a smaller quantity of a composition of hydrocarbon oligomers almost totally saturated, characterized in that the above composition of almost totally saturated hydrocarbon oligomers: 1) is obtained by the oligomerization and subsequent hydrogenation of a hydrocarbon composition comprising basically C.sub.13 -C.sub.18, preferably C.sub.15 -C.sub.16, internal oligomers, in a quantity of more than 90% by weight, 2) is basically without any possible hydrocarbons having a number of carbon atoms equal to or less than 13, 3) has a viscosity at 100.degree. C. of betweem 5.0 and 12.0 cSt, particularly from 7.3 to 8.4 cSt.