The radical cations of methyl-substituted benzene toluene, p-xylene, o-xylene, m-xylene, and their deuterated analogues generated in CFCl3 and CF3CCl3 matrices by X-ray irradiation at 77 K were investigated by ESR and high-resolution ENDOR spectroscopy. The ESR and ENDOR spectra in these radical cations are dominated by large axially symmetric hyperfine splitting due to methyl-group protons. The anisotropic hyperfine coupling constants (hfcc) of methyl protons and ring protons in radical cations of toluene and p-xylene were measured accurately by ENDOR spectroscopy. In the case of deuterated p-xylene and o-xylene radical cations in CF3-CCl3 matrix, the hyperfine coupling constants are scaled by their magnetogyric ratio (gamma(H)/gamma(D) = 6.51). Theortetical calculations of the isotropic and dipolar hyperfine coupling constants in these radical cations are found to be in good agreement with experimental results. The experimental and theoretical calculations supported the stabilization of the B-2(2g) type of state for the radical cations of toluene and p-xylene compared to the stabilization of the B-2(1g) type of ground state for o-xylene and m-xylene due to lifting of the orbitril degeneracy of the el, orbital by lowering the symmetry obtained after substitution of hydrogen by methyl group.