Partial oxidation process of liquid and/or gaseous fuels, by means of a catalytic system, preferably consisting of oxides, nitrides or oxynitrides containing one or more elements selected from Rh, Ru, Ir, Pt, Ni, Fe, Co, Cr and Cu, comprising the following steps: --premixing and, upon start-up, preheating the reagents consisting of natural gas, oxygen or air or air enriched in oxygen, optionally vapour and/or CO.sub.2, to temperatures ranging from 150 to 600.degree. C., below the flash-point values, so that the surface rate of the reaction gases is maintained above the flame rate and the temperature of the reagent mixture in the area preceding the catalytic bed is below its flash point; --reacting the reagent mixture in the reaction zone by interaction of the catalyst, activating it at temperatures ranging from 150 to 600.degree. C. and at space velocities ranging from 50,000 to 5,000,000 Nl reagents/L cat.times.h, reaching temperatures ranging from 600 to 1350.degree. C.