The influence of the presence and availability of ambient, “secondary” air on the oxidation of CO in partially premixed burner flames is considered, using laser-induced fluorescence. Composite two-dimensional images of the distributions of OH-radicals and CO-molecules in partially premixed bunsen flames, burning in the open air, arc compared with expectations based on the assumption of a closed system. The results indicate that many features of the structure of these flames arc intrinsically due to the interaction of the flame with the ambient environment. The imaging technique is further applied to elements from a burner system from a household appliance. In these experiments, the availability or secondary air is varied by changing the distance between two of the component burners. The images show a declining OH density between the burners as the distance decreases, with a concomitant increase in CO.