Changes in the thermogravimetrically determined oxidation behaviors of CVD-grown multiwalled carbon nanotubes with varying synthesis conditions are examined. Catalyst type and synthesis temperature are found to have a measurable impact upon nanotube stability, suggesting differing levels of crystalline perfection in the resulting nanotubes. The results provide evidence showing the catalytic effects of nanombe catalyst particles and their oxides upon the oxidation of nanotube carbon and graphite. The significance of thermogravimetric analysis as a characterization tool for carbon nanotubes is discussed.