NO yields are maximized at high T vib and high N radical densities and in the plasmaonly and plasma-catalytic reactors, respectively (Fig. ). In both of these regimes, a large fraction of plasma-generated N radicals ultimately return to N 2 either homogeneously or at the catalyst surface, diminishing the energy efficiency of NO production. To compare the theoretical energy consumption of the two reactors as a function of reaction species, we calculate the enthalpy required to reach T vib and P N from reactants at the bulk gas temperature, and normalize the energy to the NO production (details in Supplementary Methods). Supplementary Fig. shows the plasma-only reactor is most energy efficient at higher T vib , consistent with previous reports. The catalyzed plasma reactor is more energy efficient overall and is particularly efficient at low T vib and intermediate P N , where the energy deposited into dissociated N 2 is most effectively directed into NO. The predicted energy consumption is two orders of magnitude lower than plasma only in this regime. The minimum predicted energy consumption is 2.9 MJ/mol NO , which exceeds the minimum energy (about 0.3 MJ/mol NO ) using established estimates of the efficiencies of known processes in a N 2 -O 2 NTP. These results illustrate that the quest for optimal NO yields and optimal energy efficiency may lead to different target plasma regimes.