A semi-empirical P.P.P. type s.c.f.m.o. method has been developed to calculate, with practical accuracy, heats of atomization (at 25 °C), bond lengths, and resonance energies of benzenoid hydrocarbons. Sigma bond energies Eσb are estimated simultaneously with the pi bond energies Eπb in this method. Self-consistent field bond lengths are obtained, by minimization of the total bond energy, Eσb + Eπb, with respect to each individual bond length. The empirical resonance energies are calculated and a new term, the stabilization energy per CC bond, is introduced.