Opposed jet H-2 diffusion flames are simulated with different H-2/O-2 and NOx chemical kinetic mechanisms. The simulations with University of California, San Diego (UCSD) NOx and H-2/O-2 mechanisms are identified to have the best agreement with the experimental data. With these mechanisms, the pressure effect on NO emission of the opposed jet flame is studied and it is shown that higher pressure enhances combustion increasing the flame temperature and NO emissions. The curved opposed tubular H-2 diffusion flames are simulated and compared with the opposed jet flames. It is shown that positive curvature enhances the preferential diffusion effect and increases flame temperature and NO emission; and vice versa for negative curvature. Flame curvature can change the NO emission as much as 5.4 times for the tested cases. A detailed flame structure comparison among curved flames and planar flames demonstrates that tubular flames are slightly narrower and their maximum stretch rates are slightly higher.