Coupled cluster theory through quasiperturbative, connected triple excitations was used to obtain optimized structures, harmonic vibrational frequencies, and heats of formation for seven small molecules important to hydrocarbon oxidation. For the three systems possessing reliable experimental heats of formation, the level of agreement between theory and experiment was excellent. To achieve this level of agreement and to simultaneously minimize the theoretical uncertainty, it was necessary to apply large correlation consistent basis sets (through septuple in some cases) followed by a number of small, but nonnegligible, energetic corrections. For CO, DeltaH(f)(0)(0 K) = -27.0 +/- 0.2 (theory) versus -27.20 +/-0.04 kcal/mol (expt). For CO2, DeltaH(f)(0)(0 K) = -93.7 +/-0.2 (theory) versus -93.97 +/- 0.01 kcal/mol (expt). For HC(O)OH (formic acid), DeltaH(f)(0)(0 K) = -88.9 +/- 0.4 (theory) versus -88.7 +/- 0.1 kcal/mol (expt). For HCO, the experimental and theoretical values are in near perfect agreement, with AH(f)(0)(0 K) = 10.4 +/- 0.2 (theory) versus 10.3 +/- 2 kcal/mol (expt), although this may be somewhat fortuitous because the experimental value has a large uncertainty. For trans-HOCO, we predict a value of AH(f)(0)(0 K) = -43.9 +/- 0.5 kcal/mol, compared to the revised photoionization value of greater than or equal to-45.8 +/- 0.7 kcal/mol. Theory, however, is in good agreement with the possible experimental value of -42.7 +/- 0.9 kcal/mol suggested in the same photoionization experimental analysis. For HCO2, theory predicts a value of DeltaH(f)(0)(0 K) = -29.3 +/- 0.4 versus -30 +/- 3 kcal/mol for a recent negative-ion photoelectron measurement. For HC(O)OOH, in which case no experimental data exists, DeltaH(f)(0)(0 K) = -65.6 +/- 0.6 kcal/mol. trans-HOCO is only slightly bound (1.1 kcal/mol) with respect to the H + CO2 asymptote. HCO2 is 15.7 kcal/mol higher in energy than trans-HOCO and lies above the H + CO2 asymptote by 14.6 kcal/mol. It is only bound with respect to the OH + CO asymptote by 9.0 kcal/mol. Three widely used parametrized methods (G2, G3, and CBS-Q) were compared to the best coupled cluster heats of formation and found to differ by up to 3.2 kcal/mol.