The sooting propensities of binary mixtures of n-heptane and toluene on one hand, and isooctane and toluene on the other hand are evaluated in atmospheric laminar diffusion flames. These hydrocarbons are indeed major components of any gasoline surrogate fuel. The sooting propensities are here measured in terms of Yield Sooting Indices (YSIs). To this end, two-dimensional maps of soot volume fraction are extracted using Light Extinction Method (LEM) applied to methane diffusion flames doped with the vapors of the aforementioned mixtures. Burning in a coflowing oxidizer stream, these flames are established over the Santoro's axis-symmetric burner. The experimental setup allows the air stream to be diluted by carbon dioxide at a content normally encountered in internal combustion engines that use exhaust gas recirculation (EGR). The evolution of the sooting propensity as a function of both toluene mole fraction in the binary mixtures and CO2 content of the air stream can then be revealed. The sooting tendencies of both kinds of blends decrease in a very linear way with increasing CO2 content of the air stream. On the opposite, the sooting tendencies of isooctane/toluene blends follow a strongly non-linear relationship with the toluene mole fraction due to synergistic effects while YSIs of n-heptane/toluene blends show very linear trends. Interestingly, these trends match those observed on other configurations of diffusion flames, further strengthening the consistency of the YSI methodology. The combined effects of fuel blending and CO2 dilution are also exhibited. All these trends can be of great importance for further investigations as toluene and isooctane mole fractions found in commercially available gasoline and gasoline surrogate fuels are prone to affect soot formation through a strong synergistic effect as identified in current study. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.