In this study, experimental conditions that allow for accurate measurement of active site densities on supported vanadia catalysts by gravimetric analysis of methanol uptake were determined. Gravimetric measurements coupled with temperature-programmed desorption showed that following methanol adsorption at room temperature physisorbed methanol is present on the catalyst for methanol partial pressures greater than similar to 10(-9) Torr. The weakly bound physisorbed species could be avoided by adsorption at 373 K. Adsorption of methanol at this temperature, however, resulted in reduction of the supported vanadia layer. The saturation coverage of chemisorbed methanol was found to be higher on fully oxidized samples relative to partially reduced samples.