The potential energy surface (PES) for the reaction of the silaformyl anion (HSiO-) with C02 was studied in detail using ab initio electronic structure theory. The calculated PES, using fourth-order perturbation theory (MP4) energies with the 6-311++G(d,p) basis set, obtained at MP2/6-31++G(d,p) geometries, shows that there are two important (low-energy) paths leading to different products, Si0 + HC02- and HSi02- + C02. There are, in addition, two paths that correspond to oxygen exchanges. All four of these paths lie below the initial reactants, HSiO- + C02. The calculated potential energy surface is in good agreement with the available experimental data.