In this work, the problem for the quality of empirically determined harmonic force constants in ground electronic state benzene has been carefully reexamined, for the case when strongly. anharmonic vibrations are involved and in particular for the A(1g) (nu (1) and nu (2)) vibrational system. A numerical procedure, based on a local bond Hamiltonian representation for the C-H stretch system and a symmetrized coordinate treatment for the nu (1)(C-C) mode, has been described and applied to the determination of the harmonic F-1,F-1, F-2,F-2, and F-1,F-2, and some important (diagonal) anharmonic force constants, instead bf the traditional FG analysis. As a reference data for the determination of the required force constants, the set of experimentally observed nu (1) and v(2) fundamentals for four D-6h benzene species C6H6, C6D6, (C6H6)-C-13, and (C6D6)-C-13 have been employed. The harmonic force constants as well as harmonic frequencies obtained in this work have substantial deviations from previous determinations. Using the presently determined force constant values, a very good fit of the calculated to the experimentally observed frequencies has been achieved.