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Abstract The ocean is estimated to contribute up to ~20% of global fluxes of atmospheric nitrous oxide (N₂O), an important greenhouse gas and ozone depletion agent. Marine oxygen minimum zones contribute disproportionately to this flux. To further understand the partition of nitrification and denitrification and their environmental controls on marine N₂O fluxes, we report new relationships between oxygen concentration and rates of N₂O production from nitrification and denitrification directly measured with¹⁵N tracers in the Eastern Tropical Pacific. Highest N₂O production rates occurred near the oxic‐anoxic interface, where there is strong potential for N₂O efflux to the atmosphere. The dominant N₂O source in oxygen minimum zones was nitrate reduction, the rates of which were 1 to 2 orders of magnitude higher than those of ammonium oxidation. The presence of oxygen significantly inhibited the production of N₂O from both nitrification and denitrification. These experimental data provide new constraints to a multicomponent global ocean biogeochemical model, which yielded annual oceanic N₂O efflux of 1.7–4.4 Tg‐N (median 2.8 Tg‐N, 1 Tg = 10¹² g), with denitrification contributing 20% to the oceanic flux. Thus, denitrification should be viewed as a net N₂O production pathway in the marine environment.