Ab initio as well as density functional methods are used to investigate various reaction paths for XCO + NO (X = H, F, Cl) with a special focus on the reaction path through the collisional complex CX(O)NO, which is experimentally proposed for X = H and F. It is revealed that the dissociation channels of CH(O)NO to HNO + CO and CF(O)NO to FNO + CO have a higher barrier, while the CCl(O)NO has a dissociation barrier lower than that of the redissociation to reactants. It is expected that this channel should be the major one for the disappearance of CCl(O)NO. To gauge the relative importance of various channels of CX(O)NO disappearance, high-pressure RRKM rate constants are obtained. These results suggest the necessity of reinvestigation of a model based on experiments for the HCO + NO reaction. For the reactions of FCO and ClCO with NO, the MP2 and B3LYP stationary point structures and relative energies are in reasonable agreement with each other, whereas for the HCO + NO reaction, the MP2 level PES is markedly different from the QCISD and B3LYP counterparts.