Knowledge of the thermodynamics of ammonia reforming in complex gases should be valuable for the control of nitrocarburizing processes. In this papersome gas mixtures based on N + H + O and/or N + H + O + C systems are discussed. From the equilibrium behaviour of these gas mixtures the nitrogen potential can be derived. The relations relevant to the application of measurement with oxygen sensors are shown and some errors due to the use of published equations are indicated. The calculation of the gas chemistry was made by a mathematical model named GPRO, developed by the authors, together with a specially determined data base for complex gaseous atmospheres.