Structures and energies of cobalt carbonyls, [Co(CO)(n)](m) (m = 0, 1+, 1-) and HCo(CO)(n), have been computed at the B3LYP density functional level of theory. It is found that these complexes prefer less symmetrical structures, and marginal structural deformations can lead to large energetic changes. The calculated bond dissociation energies of [Co(CO)(n)](+) (n =1-5) are in nice agreement with the experiments, and these in turn verify the optimized structures to be the corresponding global energy minima. A spin-allowed dissociation channel is suggested for [CO(CO)(5)](+) with the loss of an equatorial CO to get the excited singlet state of [CO(CO)(4)](+). Furthermore, the bond dissociation energies of Co(CO), (n = 1-4), unavailable experimentally, are computed to aid experiments. In addition, novel structures for the most stable triplet ground states of [CO(CO)(n)](+) (n = 3, 4) and for the elusive HCo(CO)(3) are proposed. It is found that Co-CO, bond dissociation in HCo(CO)(n) (n = 1-4) is energetically more favorable than the Co-H homolysis. The structure and stability of formyl complexes, (HCO)CO(CO)(3), have also been discussed.