We present a systematic multiconfigurational study of the lowest two doublet potential energy surfaces of atomic aluminum with molecular oxygen. The most likely products, AlO and AlO2, are expected to figure prominently in subsequent reactions to form Al2O3. The main reaction pathways on both surfaces invariably lead to the formation of cyclic AlO2, possibly followed by isomerization to the lower-energy linear AlO2 isomer. A reaction path leading from Al+O-2 directly to AlO+O was not located. However, both AlO2 isomers can dissociate to AlO+O with no barrier beyond endothermicity. There is also no barrier for the reaction of AlO2 with AlO to form Al2O3, and this reaction is highly exothermic. (C) 2003 American Institute of Physics.