Preferential sputtering has been observed for NiO(100) and CoO(100) under low fluxes of 2 keV Ar +, with oxygen/metal sputtering yields a strong function of substrate temperature. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to follow the chemical and compositional nature of the surface for substrates prepared and characterized under UHV. Using O/M AES ratios as a measure of oxygen content, congruent sputtering was found for the oxides at 300 K for fluences of up to 10 17 Ar +/cm 2 and threshold temperatures for sputter reduction were observed at 350 K and 500 K for NiO and CoO, respectively. The relatively close thresholds for NiO and CoO sputter reduction argue against current thermal sputtering theory which predicts incongruent sputtering through oxygen vaporization. The temperature dependence of the O/M sputtering yields indicates that metal oxide sputtering is far more complex than current theory is able to describe. XPS data show evidence that adsorbed oxygen species, distinct from lattice oxygen, have formed on surfaces which have undergone sputter reduction and these species are postulated to play a role in the sputtering mechanism. MnO(100) crystals show no evidence for preferential sputtering for substrate temperature of up to 1000 K.