A total of 816 ab initio points at the PUMP4/6-311G(2d) level were used to derive an analytical expression for the lowest (3)A’ adiabatic potential energy surface (PES) of the reaction O(P-3)+CS(X(1) Sigma(+))-->CO(X(1) Sigma(+))+S(P-3). Thermal rate constants calculated using the variational transition state theory and semiclassical tunneling correction were used as a tool to determine the optimum analytical surface. This was done by comparing the calculated rate constant at room and lower temperatures with the experimental values. The best analytical surface (PES 3) reproduces the rate constant at low temperatures well. However, it has not been possible to obtain an analytical PES capable of reproducing both the rate constant at 300 K and the activation energy (150-300 K range) I At higher temperatures, the contribution of the lowest (3)A " adiabatic potential energy surface to the rate constant seems to be important to reproduce the experimental data. At present, the PES 3 is the most suitable analytical surface to be used for kinetic and dynamical single surface studies.