Results of a theoretical and experimental study of the structure of a counterflow diffusion flame burning diluted methane in diluted air are reported. Concentration profiles of the stable species were measured using gas sampling techniques with quartz microprobes. The samples were analyzed with a gas chromatograph. Temperature profiles were measured using coated thermocouples. Numerical calculations of the structure of the flame were performed with an adaptive nonlinear boundary value method at conditions identical to those used in the experiment. The results are compared using both the physical coordinate and the mixture fraction as the independent variable. Excellent agreement is obtained for concentration profiles of CH 4 , O 2 , N 2 , CO 2 and H 2 O and for the peak value of the temperature. The complete temperature profile and the H 2 and CO profiles are not in as good agreement and the differences are attributed to the neglect of C 2 chemistry in the numerical calculations.