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This paper presents measurements of the burning velocity of premixed CO-H2-O2-N2 flames with and without the inhibitor Fe(CO)5 over a range of initial H2 and O2 mole fractions. A numerical model is used to simulate the flame inhibition using a gas-phase chemical mechanism. For the uninhibited flames, predictions of burning velocity are excellent and for the inhibited flames, the qualitative agreement is good. The agreement depends strongly on the rate of the CO+OH↔CO2+H reaction and the rates of several key iron reactions in catalytic Hand O-atom scavenging cycles. Most of the chemical inhibition occurs through a catalytic cycle that converts O atoms into O2 molecules. This O-atom cycle is not important in methane flames. The H-atom cycle that causes most of the radical scavenging in the methane flames is also active in CO-H2 flames, but is of secondary importance. To vary the role of the Hand O-atom radical pools, the experiments and calculations are performed over a range of oxygen and hydrogen mole fraction. The degree of inhibition is shown to be related to the fraction of the net Hand O-atom destruction through the iron species catalytic cycles. The Oatom cycle saturates at a relatively low inhibitor mole fraction (~100 ppm), while the Hatom cycle saturates at a much higher inhibitor mole fraction (~400 ppm). The calculations reinforce the previously suggested idea that catalytic cycle saturation effects may limit the achievable degree of chemical inhibition. ** The reactions and increased rates were FeO+H2O↔Fe(OH)2 (kf = 1.62E+13, increased by 3X), FeOH+H↔FeO+H2 (kf = 1.50E+14 exp(-805/T), increased by 5X), Fe(OH)2+H↔FeOH+H2O (kf = 1.98E+14 exp(-302/T), increased by 3X). † † To avoid excessive repetition, references to previous calculations of Fe(CO)5-inhibited methane flames refer to Ref. [8] unless otherwise noted.