Submicron silicas produced by fumed processes and their corresponding surface-modified counterparts are compared with respect to their applicability as external additives for electrophotographic toners. The principal metric for comparison is tribo-electrostatic charge (T-ESC) stability under extended activation periods. Experimental samples are surface-modified submicron silicas produced by a fumed process. These materials have sufficient hydrophobicity and can work as spacer particles to prevent the embedding of small particle size external additives. This spacer-attribute thereby eliminates problems with charge stability and flowability, especially under extreme environmental conditions, that can impact toner performance.