Modeling of NO formation in a turbulent, nonpremixed jet flame with a fuel mixture of 31% methane and 69% hydrogen has been performed using the joint scalar probability density function (PDF) approach and the traditional flamelet model. The importance of various effects such as transients, flame interaction, preferential diffusion, and radiative heat loss on NO formation is evaluated by comparisons of predictions with experimental data. The radiative heat loss is included in the PDF approach using the optically thin limit model. A simple model to account for the effect of temperature decrease on thermal NO formation is used in the flamelet model. The model results suggest that radiative heat loss becomes increasingly important for NO predictions in the far field, and it can lower the predicted values by a factor of 3 leading to a better agreement with the experimental data. Preferential diffusion, which is not included in the PDF model, is found to be insufficient to account for the overprediction in the NO levels by the flamelet approach. Comparisons of the predicted CO concentrations from the two models indicate that transient and flame interaction may be important for describing the flame behavior in the near field.