The solid and gaseous products from the silation of powdered silica, granular silica, silica-alumina, and aluminum silicate have been determined for a range of reaction conditions. In all cases HCl was produced, as expected. Unexpectedly, lesser but significant quantities of methane were also produced at temperatures over 200 degrees C. During silation of silica at 250 degrees C methane is briefly the only gaseous product, followed by copious production of HCl and a decreasing proportion of methane. This sequence of events suggests that initially the reaction is dominated by irreversible chemisorption at highly active sites and that reaction of hydroxyls with the chlorosilane to produce HCl occurs only after the highly active sites are consumed. Silation of aluminosilicates differs from that expected from the additive effects of the surface Al-OH and Si-OH, demonstrating that the surface of the mixed support is modified compared to those of each component. Silation of a commercial silica-alumina catalyst support was very similar to that of alumina, indicating that the surface properties of this material are alumina-like and do not resemble an aluminum silicate.