The thermogravimetric method is used to study the oxidation properties of plasma grown diamond films both with and without fluorine. The oxidation experiments occur over a temperature range of 600–800 °C in pure oxygen at atmospheric pressure. Diamond films with fluorine are found more resistant (by a factor of 4 at 700 °C) to oxidation. The activation energy for oxidation, however, is a factor of at least 2.3 lower for fluorinated diamond films. Consequently, it is postulated that oxidation mechanisms for diamond films are quite different depending upon the fluorine content. Oxidation on nonfluorinated diamond films seem to proceed as a rate‐limited reaction while the oxidation of fluorinated films seems to be a diffusion limited reaction. Oxidation rates are also found to depend weakly on film density, crystal texture, and phase composition of the diamond films.