The rich surface chemistry of gold at the nanoscale has made it an important catalyst for low-temperature applications. Recent studies point to the possible role of self-organized structures formed by chemisorbed O atoms on the surface of gold catalysts for their catalytic activity and/or deactivation. In this study, we investigate the reactivity of a double O chain running along a step on a Au(221) surface with oxygen vacancies as a prototypical model of a 1D surface gold oxide. We compare CO and O₂ adsorption on such a chain with the oxygen-free Au(221) surface model. A systematic study of the reactivity of the double chain with O vacancies was done with respect to the regular Au(221) surface using CO as a probe. The CO oxidation was investigated assuming dissociative and associative mechanisms. Remarkably, O₂ adsorbs stronger on the double oxygen vacancy than on the regular Au(221) surface, and its dissociation barrier reduces significantly from 1.84 eV to 0.87 eV, whereas the CO adsorption energy is similar on these surfaces. Calculations suggest that CO oxidation should occur more efficiently on the double O vacancy than on the regular Au(221) surface due to stronger adsorption of O₂ and a low activation barrier for O₂ + CO surface reaction.