This work presents a wide range of growth rate data of thin (1-60 nm) silicon oxides grown in an ultradiluted ambient of H2O or D2O in the temperature range 750-950 degrees C. A considerable and constant difference of 18% in oxidation rate is found between the two oxidizing species. Modeling of the obtained oxidation data with the Deal-Grove, Reisman, and Wolters models results in poor fits. The extracted activation energy suggests the presence of a rapid initial oxidation regime for the first 10 nm, not incorporated in the investigated models. (c) 2005 The Electrochemical Society.