Two turbulence-chemistry interaction models that can be used in numerical modeling of oxy-natural gas dame combustion, where the reaction kinetics are fast and thermal dissociation in the products is of importance, have been compared and investigated. Detailed in-flame measurements, carried out in a coaxial jet diffusion dame of natural pas burning in pure oxygen, are presented and are used to validate the models. Both turbulent combustion models, namely, the presumed probability density function (PDF) model and the eddy dissipation concept (EDC), were combined with a chemical thermodynamic equilibrium procedure to describe the chemistry. The models differ in that, in the presumed PDF model, a statistical view point is utilized when calculating the local composition, whereas, in the EDC, the turbulent mixing rate plays a more dominant role. The calculations showed that, although the temperature field could be well predicted, the concentrations of intermediate species apl,eared too high. Similar predictions were obtained with both models, the largest differences were found in the flame sheet in the vicinity of the burner inlet. The much smaller influence of the description of the chemistry found in the dame calculations compared to that in the thermodynamic equilibrium calculations indicates that radiation has a strong smoothing effect on the results.