Nitric oxide was doped into premixed, stoichiometric, 10 torr flames of CH4/O-2/N-2, C2H6/O-2/N-2, C2H4/O-2/N-2 and C2H2/O-2/N-2. Spatial profiles of electronic ground state CH, OH, NO, CN, NCO, NH and metastable state C-3(2) were obtained by laser-induced fluorescence. The peak temperatures of the flames were maintained at 1800 K by varying the N-2 buffer gas mole fraction. Comparisons of the profiles among the different fuels illustrate differences in the hydrocarbon flame structure that lead to different NO reactivities in these flame systems. Concentrations of the nitrogen-containing intermediates are similar in the methane, ethane, and ethylene flames, but are considerably larger in the acetylene flame, indicating a much greater NO reactivity in this flame, The species profiles are modeled using three different kinetic mechanisms; all of these have significant shortcomings.