Potentials are computed for the transfer of a proton between two hydroxide anions in (HO-H-OH)− and between two neutral water molecules in (H2O-H-OH2)+ using polarized basis sets of various sizes. SCF transfer barriers are lowered in both complexes by electron correlation. As progressively higher orders of Moller-Plesset perturbation theory are applied, the correction reverses sign and diminishes in magnitude. As a consequence, MP2 results nearly coincide with full fourth-order data. The highest level calculations indicate the transfer barrier of (HO-H-OH)− exceeds that of (H2O-H-OH2)+ by 20–30%. The MP4 calculations agree well with coupled cluster CCD + ST results which include single, double, and triple substitutions to high order.