A method for determining a combustion gas composition of a combustion gas for an internal combustion engine includes operating the engine, and establishing an operating point of the internal combustion engine during operation. The method also includes detecting a nitrogen oxide emission of the internal combustion engine at the operating point. The method further includes detecting an exhaust gas temperature of the internal combustion engine at the operating point, and detecting a combustion air ratio of the internal combustion engine at the operating point. The combustion gas composition of the combustion gas is determined based on the operating point, the detected nitrogen oxide emission, the detected exhaust gas temperature and the detected combustion air ratio.