Rate constants for the reaction of chloride ion with methyl bromide have been determined over a range of buffer gas pressures from 300 to 1100 Torr at 125 degrees C by ion mobility spectrometry (IMS). The rate constants were found to increase slightly with increased pressure over this range and also increased slightly with a change from nitrogen to methane buffer gas. Parallel measurements for the reaction of chloride ion with n-butyl bromide indicated no dependence of the observed rate constants on changes in the pressure or identity of the buffer gas, as expected. The present measurements indicate that the high-pressure limit (HPL) of kinetic behavior is not achieved for the Cl-/CH3Br reaction system by use of buffer gases in the near-atmospheric pressure range and are consistent with a recent suggestion by Seeley et al. that this reaction should occur with near-collision frequency in its high-pressure limit.