Experimental results from an isothermal laminar flow reactor at atmospheric pressure are presented on the chemical composition in the post-oxidative region of two sooting fuel-rich pre-mixed mixtures diluted in nitrogen. A base case composed of n-heptane and O 2 in N 2 at 1425 K with a C/O of 2.85 was perturbed by substituting 10% of the carbon in n-heptane with carbon as CH 4 . While these changes would intuitively reduce aromatics and soot formation by increasing H 2 and decreasing C 2 H 2 concentrations, we observe the opposite. The concentrations of individual aromatic species are observed to actually increase by up to 50% and the soot yield increases by 80%.