Many combustion systems inject air into a hot fuel-rich cross-flow to minimize carbon monoxide emissions. The aim of this study is to improve the understanding of the relationship between mixing, chemical kinetics, and combustion efficiency for air jets in a hot reacting cross-flow. Carbon monoxide and hydrogen concentration measurements have been made for nine different round jet configurations issuing air into a hot reacting cross-flow. The unmixedness was measured for the 18 round jets module. The study indicates that the maximum combustion efficiency depends primarily on the overall equivalence ratio. An equivalence ratio of approximately 0.8 leads to the best combustion efficiency for all of the round jet modules, The predominance of the equivalence ratio highlights the importance of premixing prior to combustion. At constant equivalence ratio, tow momentum flux ratios yield higher emissions. The combustion efficiency improves as the number of jets increases. The same flow conditions optimized both H-2 and CO combustion efficiencies.