The 1,5-cyclooctadiene (COD) molecule can easily form complexes with transition metals with the molecular structure of various of these complexes being proposed with the aid of X-ray diffraction methods. The fact that the complexes exhibit weak metal-COD bonds makes it very important in inorganic synthesis and catalysis. In this work the potential energy surface (PES) for the COD molecule was comprehensively investigated: first with molecular mechanics (using the MM3 force field); and, in a second stage, at the ab initio Hartree-Fock level of theory employing the 3-21G*, 6-31G, and 6-31G* basis sets and also including electron correlation effects at the Moller-Plesset second-order perturbation theory level. This work revealed that there are three distinct conformers of the COD molecule with the predicted lowest energy conformation being in agreement with the proposed structure based on experimental electron diffraction data. © 1997 by John Wiley & Sons, Inc.