A transported composition probability density function (PDF) method is applied to laboratory-scale turbulent CO/H2/N2 ("syngas") flames and a 0.8 MW Oxy-Natural gas furnace. A consistent hybrid Lagrangian particle/Eulerian mesh algorithm is used to solve the modeled PDF transport equation. The model includes standard k-epsilon turbulence, gradient transport for scalars, and EMST mixing. Sensitivities of model results to the treatment of radiation heat transfer, the choice of chemical mechanism, and the PDF mixing model are explored. The model reproduces the measured mean and rms temperature, major species, and minor species profiles reasonably well. Radiation effects are relatively small in the syngas flames, but consideration of radiation is important for accurate NO prediction. The choice of chemical mechanism is also essential for the NO prediction. It is important to account explicitly for turbulence-chemistry interactions, although the details of the mixing model do not make a large difference in the results, within reasonable limits.