The effect of oxygen's activity on the rate of In-2(WO4)(3) and In6WO12 formation reactions was studied to determine the reaction mass transfer mechanism. It was established that the formation of In-2(WO4)(3) in a model reaction cell is due to the transfer of WO (4) (2-) components and electrons moving in opposite directions through the reaction product. The relation between the diffusion coefficients of the carriers was found. The rate of electron diffusion and the reaction rate were shown to vary according to the law K-p approximate to D-lim = D-e similar to a(O2)(-1/4). We conclude that the formation of electronic conductor In6WO12 is a two-region process: at the In-2(WO4)(3) | In6WO12 interface, the product is formed on the In-2(WO4)(3) surface due to {WO3} escaping toward In2O3, and at the In6WO12 | In2O3 interface, the product is formed on the In2O3 surface via the reaction of diffuse {WO3} with In2O3. The probable relationship between the diffusion coefficients of the In6WO12 components was obtained. A relation was developed for the process rate. The diffusion coefficients for the limiting component were calculated using the data on the estimated thickness of the product layers.