A tubular reactor (300; 500; 600) for carrying out exothermic oxidation gaseous reactions to produce maleic anhydride from a gas mixture containing n-butane and oxygen comprising: a first reaction zone comprising an inlet for said gas mixture and a second reaction zone comprising an outlet for a reaction gas mixture containing maleic anhydride, wherein the first reaction zone precedes the second reaction zone in a direction of flow of the gas mixture, a plurality of tubes extending in an axial direction through said first and second reaction zones (110, 120) and communicatively connected with said inlet and said outlet with respective first and second ends thereof; a temperature control system configured for controlling a reaction temperature in each of the reaction zones independently, wherein the temperature control system comprises: a heat transfer system (16, 21) for each of the reaction zones configured for controlling the temperature of a liquid coolant flowing through one of the reaction zones; and; a circulation pumping system (15, 22) configured for controlling flow conditions of the liquid coolant flowing through the reactor and through one of the heat transfer systems; and a preheating arrangement configured for preheating the gas mixture such that the gas mixture enters the first reaction zone at a predefined inlet temperature (T in); characterised in that the axial length of the tubes within said first reaction zone corresponds to between 30% and 45% of the total length covered by the tubes within said first and second reaction zones (110, 120); under the proviso that the inlet temperature (T in) and the proportions of the length of the tubes arranged in said first and second reaction zones (110, 120) are such that a total heat generated by the exothermic reactions inside the first reaction zone is equal or larger than an amount of heat required for preheating the gas mixture to the predefined inlet temperature (T in); wherein the axial length of the tubes within the first reaction zone and the settings of the preheating arrangement, the heat transfer systems (16, 21) and the circulation pumping system (15, 22) are configured such that a maximum value of the reaction temperature in the first reaction zone is equal or larger than a maximum value of the reaction temperature in the second reaction zone. a first reaction zone comprising an inlet for said gas mixture and a second reaction zone comprising an outlet for a reaction gas mixture containing maleic anhydride, wherein the first reaction zone precedes the second reaction zone in a direction of flow of the gas mixture, a plurality of tubes extending in an axial direction through said first and second reaction zones (110, 120) and communicatively connected with said inlet and said outlet with respective first and second ends thereof; a temperature control system configured for controlling a reaction temperature in each of the reaction zones independently, wherein the temperature control system comprises: a heat transfer system (16, 21) for each of the reaction zones configured for controlling the temperature of a liquid coolant flowing through one of the reaction zones; and; a circulation pumping system (15, 22) configured for controlling flow conditions of the liquid coolant flowing through the reactor and through one of the heat transfer systems; and a heat transfer system (16, 21) for each of the reaction zones configured for controlling the temperature of a liquid coolant flowing through one of the reaction zones; and; a circulation pumping system (15, 22) configured for controlling flow conditions of the liquid coolant flowing through the reactor and through one of the heat transfer systems; and a preheating arrangement configured for preheating the gas mixture such that the gas mixture enters the first reaction zone at a predefined inlet temperature (T in);