The oxidation behaviour of a number of commercially available 9 - 12 % Cr steels as well as model alloys with a systematic variation of selected alloying elements was studied at temperatures between 550 and 650degreesC. For characterizing the oxidation behaviour, the results of gravimetric studies were combined with data obtained from a number of analysis techniques, such as optical metallography, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX), Raman spectroscopy (LRS) and sputtered neutrals mass spectrometry (SNMS). The critical Cr-content for obtaining protective oxidation appeared to depend on presence of minor alloying addition and probably alloy microstructure. In the mentioned temperature range some of the studied materials exhibited a decreasing oxidation rate with increasing temperature.