Past experimental evidence has shown that acetylene and molecular hydrogen are controlling elements in the reaction bath for PAH (polycyclic aromatic hydrocarbon) growth in fuel-rich premixed combustion. The present work provides experimental evidence that the amount of methane produced from the initial fuel also plays a significant role in determining the rate of PAH formation and needs to be considered as an additional parameter for characterizing the growth environment. The experiments are performed in an isothermal laminar non-plug-flow reactor operating at atmospheric pressures. The fuel is n-heptane and serves to generate a C2H2-H-2 (and now CH4) bath for PAH and soot formation. Results are obtained at 1430 K for a base mixture consisting of 4000 ppmv n-heptane and 7000 ppmv O-2 in nitrogen (C/O=2.0) and a perturbed mixture with 3000 ppmv of added methane and decreased n-heptane to maintain the same carbon content. The substitution of carbon as n-heptane with carbon as methane causes up to a two-fold increase in the rate of benzene formation. Other PAH concentrations are also observed to increase in amounts ranging from 0 to 70% depending on the species. As a consequence, the soot mass concentration also increases. Derailed kinetic mechanisms from the literature are qualitatively capable of predicting the effect of methane and can thus provide further insight into the governing reaction pathways. Essentially the added methane promotes odd carbon numbered molecules such as propargyl and cyclopentadienyl which then promote benzene and other PAH formation.