Reaction of CO with carbonaceous surfaces was investigated using B3LYP density functional theory level (DFT) with the 6-31G(d) basis set. It was found that CO can be adsorbed exothermically on the active sites of zigzag, armchair, and tip carbonaceous models to yield stable intermediates such as cyclic ether, carbonyl, lactone, ketone, carbonate, and semiquinone functionalities. The above reactions are important in carbon gasification processes as well as in carbon single-wall nanotubes formation from CO disproportionation reaction. In the case of gasification, adsorption of CO blocks the active sites of the carbonaceous material and thus can reduce the efficiency of the process. Furthermore, it was found that when CO is adsorbed in a carbonyl type structure (CdCdO), there is a reversible interconversion process by ring closure with a neighbor active site to produce a cyclic ether (furan type), a process that requires an additional neighboring active site. Consequently, the available number of active sites for gasification reaction is decreased and therefore the gasification reaction is inhibited. In addition, CO adsorption on oxidized surfaces can favor CO 2 desorption. Such desorption can be either taking off an oxygen atom that potentially was going to be desorbed as CO or depositing a carbon atom on the surface due to the disproportionation reaction 2 CO) C + CO 2 . Both effects can inhibit or retard the gasification process. The results from the disproportionation reaction can also provide an insight into the mechanism for carbon single-wall nanotubes growth using CO as precursor.