Detailed measurements of reactive and passive scalars in axisymmetric bluff-body flames of CH4/H-2, CH4/air, and CO/H-2 have been reported in the past [1] and have been used in several studies directed at developing and validating turbulent combustion models [2-5]. Comparisons of measured and modeled results for flames with CH4/H-2 as fuel have shown significant disagreement in the mass fractions of CO, with the Raman scattering measurements of [CO] being much higher than the modeling calculations. Previously published data [1] were collected using the Raman scattering technique for all major species including CO. Raman scattering measurements of [CO] in methane flames suffer from laser-excited interference from higher hydrocarbons formed on the fuel-rich side of the reaction zone. It is well established [6-8] that measurements of [CO] based on two-photon laser-induced fluorescence (TPLIF) can provide much better accuracy than those based on Raman scattering in methane and natural gas flames. (C) 2003 The Combustion Institute. All rights reserved.