The overtone vibrational spectra of all T-d symmetry isotopomers of methane have been analyzed simultaneously. A Hamiltonian expressed in internal curvilinear coordinates expanded to the fourth order has been employed, with a nine-dimensional basis of harmonic oscillator wave functions in symmetry coordinates. Near-resonant anharmonic interactions are treated to first order, while weaker interactions are handled as second order perturbations. A set of optimized Born-Oppenheimer force constants is obtained, which reproduces the observations up to 9500 cm(-1) and shows an excellent agreement with the results of ab initio calculations.