Nitrogen oxides (NO x ≡ NO + NO 2 ) in the upper troposphere (UT) have a large impact on global tropospheric ozone and OH (the main atmospheric oxidant). New cloud-sliced observations of UT NO 2 at 450–280 hPa (~ 6–9 km) from the OMI satellite instrument produced by NASA and KNMI provide global coverage to test our understanding of the factors controlling UT NO x . We find that these products offer useful information when averaged over coarse scales (20° × 32°, seasonal), and that the NASA product is more consistent with aircraft observations of UT NO 2 . Correlation with LIS/OTD satellite observations of lightning flash frequencies shows that lightning is the dominant source of NO x to the upper troposphere except for extratropical latitudes in winter. We infer a global mean NO x yield of 280 moles per lightning flash, with no significant difference between the tropics and mid-latitudes, and a global lightning NO x source of 5.6 Tg N a −1 . There is indication that the NO x yield per flash increases with lightning flash footprint and with flash energy.