Improving the combustion of conventional and alternative fuels in practical applications requires the fundamental understanding of large hydrocarbon combustion chemistry. The focus of the present study is on high molecular weight branched alkanes, namely, 3-methylheptane and 2,5-dimethylhexane in premixed combustion systems. These structures, along with 2-methylheptane and n-octane, are important candidate surrogate components for conventional diesel fuels derived from petroleum, synthetic Fischer-Tropsch diesel and jet fuels derived from coal, natural gas, and/or biomass, and renewable diesel and jet fuels derived from the thermochemical treatment of bio-derived fats and oils (e.g., hydrotreated renewable jet (HRJ) fuels). This study presents a novel low and high temperature chemical kinetic model for the oxidation of the aforementioned fuels. The proposed model is validated against new experimental data from a premixed flame and perfectly stirred reactor. Significant effort is placed on the understanding of the effects of methyl substitution on important combustion properties such as laminar flame speed, low temperature reactivity, and species formation.