The adsorption and desorption behavior of cationic dialkyldimethylammonium bromide surfactants (Di-CnDABs where n = 10, 12, 14) at the silica-toluene interface has been studied. Adsorption is a rapid process, consistent with transport control, whereas desorption appears to occur in a two-stage process, with varying proportions of surfactant desorbing in fast and slow modes. These proportions appear to be affected by trace moisture present ill the adjacent toluene solvent, possibly owing to competition between surfactant and water molecules for surface sites. Surprisingly, the surfactant tail length (n) has a significant impact oil solubility in toluene, and this appears to affect bulk-surface partitioning. The results are compared with previous experiments utilizing nonionic surfactants (Tabor, R. F.; Eastoe, J.; Dowding, P. Langmuir 2009, 25, 9785), and also with work on surfactant-stabilized silica in nonpolar solvents (Tabor, R. F.; Eastoe, J.; Dowding, P. J.; Grillo, I.; Heenan, R. K.; Hollamby, M. Langmuir 2008, 24, 12793). Observations are explained in terms of the balance of interactions between the surfactant, solvent, and surface.