The surface reactivity of amorphous (Ti 0.5Cu 0.5) 0.9Al 0.1 alloys has been probed using thermal oxidation and plasma oxidation studied with XPS and Auger depth profiling techniques. The aluminum concentration at the surface of the initial air-passivated sample was greatly enhanced relative to the bulk alloy composition while that of copper was reduced substantially. Thermal oxidation at temperatures above 400°C at 5 or 500 mTorr oxygen pressure increased the surface composition of titanium while reducing that of aluminum and completely eliminating surface copper. In contrast, the surface metal composition produced during plasma oxidation at temperatures between 200 and 500°C with 30mTorr oxygen partial pressure approximated more closely that of the bulk alloy. In the plasma oxidation only the highest oxidation state corresponding to CuO is present at temperatures below 400°C. An observed shift in the 2p binding energy of Ti 4 suggests crystallization of the amorphous TiO 2 surface layer at 200–300°C during thermal oxidation, but this crystallization was found to be hindered by plasma oxidation. The results are discussed in terms of their importance to catalysis and corrosion.