Various isomers with the constitution OSiCO are located with ah initio MP2 as well as B3LYP methods using 6-311G(d) basis sets. On the singlet potential surface, the van der Waals complex OSi ... CO is calculated to be most stable. This molecule has a planar structure in which the SiO and CO subunits are arranged between a perpendicular and a parallel configuration. The bent Si-OCO complex and trans-OSiCO molecule are the most stable species on the triplet energy surface. A modified version of the G2/MP2 method has been used to obtain energies of high accuracy, The vibrational frequencies of all the isomers are predicted.