The invention relates to a hydrocarbon composition, which can be used as a fuel and/or fuel oil, containing a petroleum component (A) and a component of a biological origin (B), wherein the component of a biological origin is present in a quantity of up to 75% by volume with respect to the total composition. Said component of a biological origin (B) is prepared starting from a mix of a biological origin (C) containing esters of fatty acids, with possible aliquots of free fatty acids, by means of a process which comprises the following steps: 1) hydrodeoxygenation of the mix of a biological origin; 2) hydroisomerization of the mix resulting from step (1), after possible water and gas flow separation, wherein said hydroisomerization is preferably carried out in the presence of a catalytic system comprising: a) a carrier of an acidic nature, comprising a completely amorphous micro-mesoporous silica-alumina, with a SiO2/Al2O3 molar ratio ranging from 30 to 500, a surface area larger than 500 m2/g, a pore volume ranging from 0.3 to 1.3 ml/g, an average pore diameter smaller than 40 Å, b) a metal component containing one or more metals of group VIII, possibly mixed with one or more metals of group VIB.