A new ab initio ground state potential energy surface (PES) for the OH + CO --> H + CO, reaction is presented. A modified Shepard interpolation method has been used to construct the PES, based on electronic structure calculations on a set of data points generated iteratively. Quasiclassical trajectory calculations yield cross-sections for the OH + CO reaction that are much smaller than found experimentally, but the energy dependence of the cross-sections for the reverse H + CO2 reaction is in qualitative agreement with experiment, thanks to the incorporation of a trans-H . OCO barrier in the PES. (C) 2004 Elsevier B.V. All rights reserved.