A process for producing synthesis gas starting from liquid hydrocarbon feedstocks, comprising at least the following operations: 1) pre-heating a stream of liquid hydrocarbon feedstocks, 2) nebulizing and/or vaporizing the stream of the pre-heated liquid hydrocarbon feedstock, at a temperature ranging from 50 to 500°C and a pressure of 0.2 to 5 MPa (2 to 50 atm), consisting of one or more of the following hydrocarbons: - naphthas, - various kinds of gas oils, such as LCO, HCO and VGO, - other products of refining cycles and oil up-grading, such as DAOs, - other heavy residues, the nebulisation being effected with the help of a gaseous propellant selected from vapour and/or a gaseous hydrocarbon, and resulting in the formation of a nebulized and/or vaporized liquid hydrocarbon stream; 3) mixing the nebulized and/or vaporized liquid hydrocarbon stream coming from phase 2) with: a) an oxidizing stream, b) a gaseous hydrocarbon stream, at a temperature ranging from 50 to 500°C and a pressure of 0.2 to 50 MPa (2 to 50 atm), with the formation of a possibly biphasic liquid-gas reaction mixture; 4) passing the reaction mixture coming from phase 3) through at least a first structured catalytic bed with the formation of a mixture of reaction products comprising H 2 and CO, said at least a first structured catalytic bed comprising a catalytic partial oxidation catalyst, arranged on one or more layers, the reaction mixture flowing through each of the layers with a contact time varying from 0.1 to 100 ms; 5) passing the mixture of reaction products comprising H 2 and CO coming from phase 4) through a final catalytic bed with a differentiated filling, comprising a catalyst capable of completing the partial oxidation reactions and promoting the steam reforming and/or CO 2 reforming reactions, with a contact time ranging from 1 to 1,500 ms. 6) cooling the mixture of reaction products coming from phase 5). 1) pre-heating a stream of liquid hydrocarbon feedstocks, 2) nebulizing and/or vaporizing the stream of the pre-heated liquid hydrocarbon feedstock, at a temperature ranging from 50 to 500°C and a pressure of 0.2 to 5 MPa (2 to 50 atm), consisting of one or more of the following hydrocarbons: - naphthas, - various kinds of gas oils, such as LCO, HCO and VGO, - other products of refining cycles and oil up-grading, such as DAOs, - other heavy residues, the nebulisation being effected with the help of a gaseous propellant selected from vapour and/or a gaseous hydrocarbon, and resulting in the formation of a nebulized and/or vaporized liquid hydrocarbon stream; - naphthas, - various kinds of gas oils, such as LCO, HCO and VGO, - other products of refining cycles and oil up-grading, such as DAOs, - other heavy residues, the nebulisation being effected with the help of a gaseous propellant selected from vapour and/or a gaseous hydrocarbon, and resulting in the formation of a nebulized and/or vaporized liquid hydrocarbon stream; 3) mixing the nebulized and/or vaporized liquid hydrocarbon stream coming from phase 2) with: a) an oxidizing stream, b) a gaseous hydrocarbon stream, at a temperature ranging from 50 to 500°C and a pressure of 0.2 to 50 MPa (2 to 50 atm), with the formation of a possibly biphasic liquid-gas reaction mixture; a) an oxidizing stream, b) a gaseous hydrocarbon stream, 4) passing the reaction mixture coming from phase 3) through at least a first structured catalytic bed with the formation of a mixture of reaction products comprising H 2 and CO, said at least a first structured catalytic bed comprising a catalytic partial oxidation catalyst, arranged on one or more layers, the reaction mixture flowing through each of the layers with a contact time varying from 0.1 to 100 ms; 5) passing the mixture of reaction products comprising H 2 and CO coming from phase 4) through a final catalytic bed with a differentiated filling, comprising a catalyst capable of completing the partial oxidation reactions and promoting the steam reforming and/or CO 2 reforming reactions, with a contact time ranging from 1 to 1,500 ms. 6) cooling the mixture of reaction products coming from phase 5).