An additive composition improves the stability and the engine performances of gas oils, including gas oils of the non-road type in compliance with the decree of 10 Dec. 2010. The additive composition includes: at least one metal deactivator or chelating agent, at least one antioxidant of the hindered phenol type (alkylphenol), at least one dispersant and/or detergent, and at least one metal passivator, wherein the composition includes improved properties, in particular relative to the oxidation resistance, storage stability, thermal stability, reduction in fouling of the injectors, reduction in loss of power, reduction in the tendency of filters to clog.