The decomposition of CF4and of O2and the formation of the plasma product molecules CO2and COF2have been determined by mass spectrometry for a 2450‐MHz CF4plasma to which variable amounts of oxygen were added. In addition, the SiF4production resulting from the interaction of the plasma effluent with a silicon wafer was monitored. It was found that up to its maximum the decomposition of CF4is twice the amount of decomposed oxygen. This result, combined with those of experiments in which CO2was used instead of oxygen, and experiments in which CF4and O2were discharged separately, leads to the conclusion that after decomposition of O2to O atoms and of CF4to CF3fragments and F atoms, one oxygen atom reacts with one short‐lived CF3fragment to form the primary products COF2and atomic fluorine. At higher oxygen concentrations, excess O(1D) atoms are formed. These atoms rapidly react with the COF2to form CO2and F2. Consequently, the COF2production strongly decreases with the simultaneous formation of carbon dioxide. At these higher oxygen concentrations it is also found that excess molecular oxygen reacts with the atomic fluorine produced, eventually forming molecular fluorine. As a result, the production of SiF4decreases much more strongly than expected on the basis of the decomposition of CF4.