In this numerical work, two-dimensional rich premixed laminar methane-air flames are calculated in detail. Emphasis is laid on the comparative analysis of spatial distributions of CO concentrations and temperature for a range of mixtures using two reaction mechanisms, and thereby reporting on the suitability of such mechanisms. A test analysis showed that the results from the present numerical scheme are in close agreement with the corresponding CHEMKIN calculations ( see Appendix). Computed results are compared with experimental data of Datta et al. ( 2004), with detailed study on equivalence ratio phi = 2.0 flame. Firstly, simulations are conducted on a relatively detailed Smooke mechanism involving 16 reactive species/46 reactions steps. Measured and calculated data are in good agreement in terms of spatial distributions as well as peak values of CO concentration and temperature for cases of phi's 1.7, 2.0, and 2.5. As a second study, a reduced mechanism ( 16 reactive species/25 reactions) is found selectively suitable for richer cases phi = 3.0 and 4.0, yielding good quantitative agreement for CO concentration and temperature. For the case of phi = 2.0, CO distributions are particularly rendered well in the inner flame zone. However, a significant difference in the CO concentration is noticed near the diffusion flame zone. The estimated CO concentration reaches a maximum distance of 8.5 mm in the lateral direction away from the axis line, while the experimental values fall to zero at 6 mm. Calculations exhibit acceptable trends at all elevated flame heights, and maximum CO concentration and temperature as experiments, showing that with the increase in equivalence ratio the flame height increases, and that the maximum CO concentration decreases.