A new semi-empirical mechanism for n-heptane oxidation and pyrolysis has been developed and validated against several independent data sets, including new flow reactor experiments. Previous semi-empirical chemical kinetic mechanisms assumed that a generic n-alkyl radical, formed by abstraction of an H-atom from the parent fuel, thermally decomposes into a fixed ratio of methyl and propene. While such an approach has been reasonably successful in predicting premixed, laminar flame speeds, the mechanism lacks sufficient detail to quantitatively capture transient phenomena and intermediate species distributions. The new chemical kinetic mechanism retains significantly more detail, yet is sufficiently compact to be used in combined fluid-mechanical/chemical kinetic computational studies. The mechanistic approach is sufficiently general to be extended to a wide variety of large linear and branched alkane fuels.