The effect of silicon precursor source concentration and oxidant composition on the specific surface area of flame made nanostructured silica particles was investigated in a diffusion flame reactor. Hexamethyl-disiloxane (HMDS) and octamethylcyclotetrasiloxane (OMCTS) were used as the organometallic Si sources along with SiCl4. As oxidant various oxygen-nitrogen mixtures and as fuel methane were used. Particles generated by oxidation of organometallic compounds tend to have a smaller specific surface area than the ones made by employing SiCl4 as precursor. This is attributed primarily to the increase of the flame temperature by the additional fuel coming from the organometallic compound. This effect is further pronounced with increasing precursor concentration as it was shown with experiments in a premixed flame reactor.