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This study proposes a skeletal kinetic mechanism to investigate the formation of C3–C4hydrocarbons, carbonyls, and aromatic hydrocarbons from the nonpremixed combustion of ethyl propionate (EP), a biodiesel surrogate. The computational procedure started with the shrinking of an existing detailed EP mechanism to generate a minimized but functionally equivalent mechanism that was then used to combine with previously published submodels that describe polycyclic aromatic hydrocarbons (PAHs) and related compounds. The newly derived EP–PAH mechanism consisting of 79 species and 469 reactions was refined and systematically validated against results of the detailed EP mechanism as well as experimental data. Incorporated into a 2-D axisymmetric laminar finite-rate model, the EP–PAH mechanism without empirical adjustment of the kinetic parameters reproduces concentration profiles in accordance with mass-spectrometrically measured centerline mole fractions of four nonfuel hydrocarbons, three carbonyls, and six aromatic hydrocarbons in the diffusion flame of methane doped with EP. The computational results can be used to interpret experimental PAH data using representative species that are unavailable in the previously published mechanism of EP oxidation. Furthermore, the concentration contour diagrams and reaction pathway analysis reveal the correlation between the decomposition of EP and the formation of the investigated products.