In this paper, we report on the oxidation behavior of Ti3GeC2 and Ti-3(Ge-0.5,Si-0.5)C-2. The oxidation kinetics were studied thermogravimetrically in air in the 700-1000 degrees C temperature range. The oxidation layers formed on Ti3GeC2 at 700 degrees C were protective; at 800 degrees C and higher, they were not. The addition of Si to Ti3GeC2 slightly enhanced its oxidation resistance, but at 800 degrees C and above, the layers formed were again not protective. In both cases the oxidation occurred mostly by the inward diffusion of oxygen through a rutile-based (Ti1-y,Ge-y)O-2 solid solution with y < 0.1. At higher temperatures and/or longer times, Ge accumulation was observed at the oxide/carbide interface. At 900 degrees C and higher, however, the oxygen induces the peritectic decomposition of Ti3GeC2 into Ge and, presumably, a titanium oxycarbide. At 1000 degrees C, part of the Ge escapes to the surface and forms copious amounts of GeO2 whiskers with hexagonal symmetry. In the temperature range explored there is no oxygen dissolution in the carbide matrices. (c) 2006 The Electrochemical Society.