The process + equipment cost and synthesis energy consumed per 1 ton NH3 were calculated over 100-300 bar as a function of final NH3 separation temp., synthesis system pressure drop, and inerts and NH3 contained in inlet and outlet gases, resp. Over 140-220 bar, the cost curve was fairly flat. The cost and energy were min. at 180 and 120 bar, resp., the shift being due to the lower reactor + catalyst cost. At 100 bar, synthesis gas could be compressed by a single-stage compressor, but synthesis gas circulation and NH3 refrigeration would consume 40% and 100% more of energy, resp. At < 100 bar, only a low-temp. catalyst (like Fe-Co or Ru) offering higher yields, could make synthesis profitable provided an energy-effective way to separate NH3 from reaction gas is developed.