Quantum mechanical cross-sections for the collinear S(N)2 reactions Cl-+ CH3Cl' --> ClCH3C + Cl'(-) and Cl- + CH3Br + ClCH3 + Br- have been calculated within the time-independent hyperspherical coordinate approach employing two-dimensional CCSD(T) potential energy surfaces. Compared to the results obtained from the potentials of Hase and co-workers, the recent cross-sections show several different features. However, the cross-sections calculated using the CCSD(T) potential energy surface for Cl- + CH3Br do not explain the experimentally observed independence of the rate constant on initial CH3Br temperature.