Nano-oils synthesized by dispersing dielectric nanostructures counter common intuition as such nano-oils possess substantially higher positive dielectric breakdown voltage with reduced streamer velocities than the base oils. Nano-oils comprising stable and dilute homogeneous dispersions of two forms of titanium (IV) oxide (TiO2) nanoparticles (Anatase and Rutile) have been experimentally examined and observed to exhibit highly enhanced dielectric breakdown strength compared to the conventional transformer oils. The present study involves titania dispersed in two different grades of transformer oils, both with varied levels of thermal treatment, to obtain consistent and high degrees of enhancement in the breakdown strength, as well as high degrees of increment in the survival of the oils at elevated electrical stressing compared to the base oils, as obtained via detailed twin parameter Weibull distribution analysis of the experimental observations. The experimental results demonstrate higher augmented breakdown strength for Anatase compared to the Rutile phase of titania. In-depth survey of literature indicates that mostly Rutile based oils are used. However, the present study shows that they exhibit relatively less breakdown strength enhancement compared to the Anatase based oils. It is also observed that heat treatment of the nano-oils further enhances the dielectric breakdown performance. The differences in the performance of Anatase and Rutile has been explained based on the electronic structure of the two and the affinity towards electron scavenging and the theory has been found to validate the experimental observations. © 2016 IEEE.