Measures reducing the NO formation by qualified firing (primary measures) are intensively investigated Fundamental elements in this context are the staging of fuel and combustion air as well as the recirculation of exhaust gas, to control residence time and also temperature and concentration patterns. For prediction, but also for optimization and central of technical combustion processes, simplified models of NO formation are applicable and required. These models should be simplified in a way that allows on-line operation and is capable of reflecting sufficiently the process. The structure of such a model (kinetics, reactors) is described in the present paper. Introducing two model parameters (a characteristic process temperature and a fuel-NO parameter), the model has proved effective in predicting NO formation during combustion of natural gas and also visbreaker residue.