The chemical vapor codeposition (CVD) of silica, alumina, and aluminosilicates from mixtures of silicon tetrachloride or methyltrichlorosilane (MTS), aluminum trichloride, carbon dioxide, and hydrogen is addressed, and detailed homogeneous and surface reaction mechanisms that describe the chemistry of the codeposition process are formulated. Information obtained from the thermodynamic analysis of the equilibrium of the gas phase and from past experimental and theoretical studies is employed to determine which elementary reaction steps play an important role in the deposition process. Homogeneous and heterogeneous chemistry models that were formulated in past studies by us for the deposition of silica and the deposition of alumina from mixtures of chlorosilane (silicon tetrachloride or MTS) and aluminum trichloride, respectively, in carbon dioxide and hydrogen are used as submodels in the codeposition mechanism. Experimental data obtained in a hot-wall, CVD reactor in our laboratory are used to validate the predictions of the codeposition model. A comprehensive study of the effect of the operating conditions (e.g., temperature) and residence time on the variation of the gas-phase composition, surface species coverages, and deposition rate is conducted in the range of conditions employed in the experiments. The model is found to be capable of predicting most of the behavior patterns observed in the experiments, including those of the enhancement of the deposition rate of silica in the presence of AlCl3 in the feed, the suppression of the incorporation rate of alumina in the deposit in the presence of silane species in the feed, and the higher rate of codeposition and deposition rate of silica from MTS.