A self-consistent set of thermochemical parameters for more than 30 molecules in the Si-O-H-C system are obtained from a combination of ab initio electronic structure calculations and empirical corrections. Heats of formation are estimated for another 15 species. The species are primarily methoxy- and ethoxysilicon compounds, including both stable and radical species as well as a few transition states. In the few cases where comparisons with experimental data in the literature are possible, there is good agreement with the calculated values. The energetics of Si(OC2H5)(4) (TEOS) decomposition reactions show that it is likely to decompose via the four-center elimination of ethylene while Si(OCH3)(4) decomposes via different reactions. This thermochemical and kinetic information will advance the modeling of the chemical vapor deposition of silicon oxide films from Si(OC2H5)(4).