Time-resolved mass spectrometry was used for analysis of the plasma reactions in radio frequency (RF) SiCl4 and SiCl4-O-2 discharges as functions of starting partial pressure and electrical power. Molecular concentrations of the reactants and products from SiCl4 alone and with O-2 were obtained from the mass spectra and used for plotting the kinetic curves. The SiCl4 and O-2 consumption rates were calculated from the kinetic curves and compared with results of theoretical simulation of the reaction. Dir ect electron impact decomposition was found to be the main pathway for pure SiCl4 conversion. On the contrary, the consumption of SiCl4 in the SiCl4+O-2 mixtures was largely chemical. The experimental macrokinetics are in agreement with a model in which oxidation is caused by the atomic oxygen.