A detailed surface reaction mechanism is formulated for the deposition of SiO2 from SiCl4/CO2/H-2 and CH3SiCl3/CO2/H-2 mixtures. The heterogeneous mechanism is coupled to a homogeneous model developed in a past study for the decomposition of chlorosilanes in CO2 and H-2, and the overall kinetic model is introduced into the transport and reaction model of a plug-flow reactor. The model is employed to investigate the sensitivity of the predicted deposition rates, surface coverages of adsorbed species, and gas-phase composition on the residence time in the reactor and the operating conditions. It is found that the concentrations of the gas-phase species (silicon species and oxygen species) that are responsible for silica deposition are strongly influenced by the occurrence of the heterogeneous reactions, and this in turn leads to strong dependence of the deposition rate profile on the reactor geometry (deposition surface to reactor volume ratio). For comparable silicon and oxygen loadings of the feed, the concentrations of the deposition precursors are much higher when methyltrichlorosilane (MTS) is used as silicon source. As a result, the rate of silicon oxide deposition from MTS can be higher by a few orders of magnitude. Experiments on silica deposition conducted in our laboratory showed that this is indeed the case, and that the overall transport and reaction model was found to be capable of reproducing, both qualitatively and quantitatively, all results obtained in those experiments.