Inverse gas chromatography is currently used for the determination of the surface properties of divided solids by probing the surface with alkanes or polar molecules of known properties. This paper suggests the use of a new topological index for the description of the probe’s (alkanes) geometry and hence of their accessibility to the solid’s surface. The proposed index (chi(T)) derives from the well known Wiener index. The application of chi(T) for the determination of the dispersive component of the surface energy of pyrogenic silica, but also for the evaluation of the geometric heterogeneity of lamellar silica, is described. Further, goethite and zirconia samples were submitted to similar analysis.