Grazing lands in the northern Great Plains of North America are extensive, occupying over 50 Mha.  Yet grazing land contributions to, or mitigation of, global warming potential (GWP) is largely unknown for the region.  The objective of this study was to estimate GWP for three long-term (70 to 90 yr) grazing management systems in the northern Great Plains.  Fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) were measured using static chamber methodology over a period of three years within a moderately-grazed pasture (MGP), heavily-grazed pasture (HGP), and a fertilized crested wheatgrass (Agropyron desertorum (Fisch. ex. Link) Schult.) pasture (FCWP) near Mandan, ND.  Carbon dioxide efflux was greatest in FCWP and least in HGP, and was strongly related to variations in soil temperature.  All three pastures were minor sinks for CH₄, averaging 1.9 kg CH₄-C ha^-1 yr^-1.  Emission of N₂O within FCWP was over twice that observed in MGP and HGP.  The majority of annual N₂O emission across all pastures occurred during brief mid-winter warming periods when air temperatures exceeded 0°C.  Using long-term estimates of soil carbon accrual ranging from 0.29 to 0.55 Mg C ha^-1 yr^-1, all three pastures were found to be net sinks when expressed on a GWP basis.  Based on results from this three year study, native vegetation pastures and seeded crested wheatgrass in the northern Great Plains appear to mitigate net greenhouse gas emissions from agriculture by serving as sinks for atmospheric CO₂.