We present a new analytical representation of the lowest 3 A‘ energy surface for the reaction O(3 P)+HCl(X  1Σ+)→OH(X  2Π)+Cl(2 P). This surface is derived by fitting a b i n i t i o calculations, and adjustments are made to the barrier height so that rate constants derived from accurate quantum scattering calculations match the room temperature thermal rate constants. Contributions to thermal and state resolved rate constants arising from reaction on the lowest 3 A’surface are also considered. Comparisons of thermal and state resolved rate constants with experiment are good except at high temperature where the 3 A’ contributions are significant.