Automotive lean-NOx has become one of the major issues in catalysis research, due to increased environmental concerns. In the present study the NOx storage/release concept has been investigated with respect to the NOx release kinetics. The importance of the gas composition during NOx release, including the lambda -value, humidity, O-2, and CO2 concentration, was studied in flow reactor experiments performed with a commercial, noble metal BaO type catalyst. The main conclusions are that CO2 has a promoting and O-2 a blocking effect on the NO, release.