Flame length and CO measurements have been conducted on different geometrical configurations issuing air through the circumferential openings in a reacting cross-flow. The main application of the research is to improve the understanding of jet mixing in a reacting cross-now in order to optimize the design of combustors used to destroy combustible exhaust gases from steel-melting furnaces, Current combustor designs are characterized by poor mixing with the combustion air entering through a gap (circumferential slit), deflecting the main flow and slowly mixing via turbulent diffusion. Alternate air inlet geometries have been studied by investigating the mixing of various circumferential air jets configurations into a high temperature combusting cross-flow. The experimental results show that the flame length decreases with increasing jet mass now. The carbon monoxide combustion efficiency dues not follow the same trend. All configurations exhibit optimum combustion efficiency at the momentum flux ratio that corresponds to the non-reacting optimum mixing conditions. Jet configurations with higher design momentum flux ratios have improved combustion efficiencies. These results suggest that furnace exhaust gas combustor designs that follow thr non-reacting optimum mixing design equations have optimal CO combustion efficiencies.