A two-fold mass spectrometer study of the Al + H2O reactions in effusion cells and in atmospheric H2+ O2 flames was conducted. The flame studies yielded a D°0 of 119.5±5 kcal/mole for AlO, in agreement with the results of previous thermochemical and spectroscopic investigations. A discussion concerning the discrepancy between the data obtained in these and previous flame experiments is presented. The major Al–O–H species in both the effusion and the flame studies was AlOH, with a ΔHf298 of –42.7±2 kcal/mole. The flame studies also produced other suboxides of aluminum, as well as the species AlO2H, for which a ΔHf298 of –90±5 kcal/mole was obtained.