System for controlling the emissions of an internal combustion engine, in particular of an air-supercharged internal combustion engine, said engine comprising an exhaust system comprising, from upstream to downstream in the flow direction of the combustion gases from the engine: an exhaust manifold, a combustion gas oxidation catalyst, a catalyst for the selective reduction of the nitrogen oxides, and comprising, upstream of said oxidation catalyst, an oxidizing gas feed device (15, 21) connected to said manifold and a means (16, 22) for regulating the flow rate of oxidizing gas supplied to said manifold, and upstream of the oxidizing gas feed device (15, 21), means for determining an oxidizing gas concentration parameter, for example an O 2 concentration parameter, of the combustion gases circulating in said exhaust manifold, and optionally means for determining a temperature parameter of the combustion gases circulating in said exhaust manifold, the control system being able to be connected to the engine and to said exhaust system, characterized in that the control system is arranged in order to control the ratio of the [NO 2]/[NO x] concentrations at the inlet of the selective reduction catalyst and comprises: - means for receiving: an oxidizing gas concentration parameter, for example an O 2 concentration parameter, of the combustion gases, optionally a temperature parameter of the combustion gases, said parameters being supplied by said determining means, characteristic parameters of an operating point of the engine, o memorizing means arranged to store at least one map and at least one model that make it possible to correlate an operating point of the engine with an amount of oxidizing gas to be supplied to the oxidation catalyst as a function of a temperature of the combustion gases, - treatment means arranged to adjust the ratio of the [NO 2]/[NO x] concentrations at the inlet of the selective reduction catalyst as a function of the operating point of the engine and optionally of the temperature of the combustion gases and to determine, from the maps recorded in the memorizing means and as a function of said characteristic parameters of the operation of the engine, of said oxidizing gas concentration parameter of the combustion gases and optionally of said temperature parameter, an amount of oxidizing gas to be added to the combustion gases via the feed device (15, 21), and to generate a corresponding control signal, - means for transmitting a control signal to the means (16, 22) for regulating the flow rate of oxidizing gas. - means for receiving: an oxidizing gas concentration parameter, for example an O 2 concentration parameter, of the combustion gases, optionally a temperature parameter of the combustion gases, said parameters being supplied by said determining means, characteristic parameters of an operating point of the engine, o memorizing means arranged to store at least one map and at least one model that make it possible to correlate an operating point of the engine with an amount of oxidizing gas to be supplied to the oxidation catalyst as a function of a temperature of the combustion gases, an oxidizing gas concentration parameter, for example an O 2 concentration parameter, of the combustion gases, optionally a temperature parameter of the combustion gases, said parameters being supplied by said determining means, characteristic parameters of an operating point of the engine, o memorizing means arranged to store at least one map and at least one model that make it possible to correlate an operating point of the engine with an amount of oxidizing gas to be supplied to the oxidation catalyst as a function of a temperature of the combustion gases, o memorizing means arranged to store at least one map and at least one model that make it possible to correlate an operating point of the engine with an amount of oxidizing gas to be supplied to the oxidation catalyst as a function of a temperature of the combustion gases, - treatment means arranged to adjust the ratio of the [NO 2]/[NO x] concentrations at the inlet of the selective reduction catalyst as a function of the operating point of the engine and optionally of the temperature of the combustion gases and to determine, from the maps recorded in the memorizing means and as a function of said characteristic parameters of the operation of the engine, of said oxidizing gas concentration parameter of the combustion gases and optionally of said temperature parameter, an amount of oxidizing gas to be added to the combustion gases via the feed device (15, 21), and to generate a corresponding control signal, - means for transmitting a control signal to the means (16, 22) for regulating the flow rate of oxidizing gas.