The pulsed field ionization zero-kinetic-energy (PFI-ZEKE) spectra of o-, m- and p-xylene have been recorded and analyzed. These clearly demonstrate neighboring methyl groups to be interacting and further apart groups to be noninteracting. The spectra show well-resolved features, typically within 150 cm(-1) of the S-1 --> ion origins, which are assigned to transitions associated with the internal rotations of the ring methyl groups. The observed transitions are fit using a one-dimensional periodic potential with a free rotor basis. The results of the analysis show that the potential barrier to methyl rotation in the xylene ion increases in the order para ( meta < ortho and that the barriers differ from those determined for the So and S1 neutral state in significant ways. This is particularly true for the interacting groups of o-xylene. The two methyl groups of p- and m-xylene are determined to be noninteracting whereas the methyl groups of o-xylene interact strongly. The ionization potentials for o-, m-, and p-xylene are also derived from the PFI-ZEKE spectra.