Inverse gas chromatography (IGC) at infinite dilution was used to characterize the fumed silica surface. The silica was modified by chemical treatment with either dimethyldichlorosilane or trimethylchlorosilane. To observe the silica and poly(dimethylsiloxane) (PDMS) interactions, we used apolar (alkanes) and polar probes (chloroform, benzene, tetrahydrofuran, etc.), but also model molecules of PDMS such as linear and cyclic oligomers of PDMS with two to five monomer units. It is shown that PDMS oligomers are very appropriate to discriminate the silylated silicas.