Reaction pathways for methane partial oxidation (MPO) on silica were theoretically investigated using the semiempirical MOPAC-PM3 molecular orbital method. The surface of SiO2 was modeled by a helical Si6O18H12 molecular cluster that also exhibits a strained siloxane bridge defect. First, a bond energy analysis was performed on the silica cluster with isolated 3- and 4-coordinated Si surface atoms. Calculated bond dissociation energies for Si-H, SiO-H, and SI-OH were comparable to H-CH3, H-OH, and O-O. In the second phase, elementary reactions around the bridge structure were studied. The facile ring-opening reaction with water, which reconstitutes a pair of vicinal hydroxyls, was found both thermodynamically and kinetically favored, in good agreement with the experiment and other theoretical methods. Activation of methane by the lattice bridge oxygen was thermodynamically unfavorable with high activation energy. On the other hand, the computational results also confirmed the important role adsorbed or "activated" oxygen plays in an MPO reaction, and indicated the likely formation of methanol as an intermediate in formaldehyde production.