The reaction of CN radicals with O-2 was studied using infrared diode laser absorption spectroscopy. CO and CO2 products were detected directly, while the yield of NCO products was inferred by measuring the N2O yield upon addition of excess NO. Experiments and kinetic modeling calculations were performed to examine the extent of secondary chemistry in this system. The following branching ratios of the CN + O-2 reaction at 296 K were determined: phi(N+CO2) = 0.02 +/- 0.01 and phi(CO+NO) = 0.22 +/- 0.02. The branching ratio into the CO + NO channel has a strong negative temperature dependence over the range 239-643 K.