Inverse gas chromatography (IGC), at infinite dilution conditions, is a very sensitive method for the monitoring of changes in the surface properties of divided solids submitted to thermal or chemical treatments. For instance, the evaluation of the surface activity of fumed silica samples, prepared by controlled silylation, is a key for the tailoring of silicas used as fillers in the (polydimethylsiloxane) PDMS elastomer industry. The aim of the present work is to demonstrate how IGC measurements, using PDMS oligomers as specific molecular probes, are suitable to illustrate the strong influence of the degree of silylation upon the surface properties of a fumed silica.