This dataset provides in situ atmospheric oxygen and carbon dioxide concentrations measured by the NCAR Airborne Oxygen Instrument (AO2) during airborne campaigns conducted by NASA's Atmospheric Tomography (ATom) mission. The AO2 Instrument measures O2 concentration using a vacuum-ultraviolet absorption technique. ATom deploys an extensive gas and aerosol payload on the NASA DC-8 aircraft for a systematic, global-scale sampling of the atmosphere, profiling continuously from 0.2 to 12 km altitude. Flights occurred in each of 4 seasons from 2016 to 2018. Flights originate from the Armstrong Flight Research Center in Palmdale, California, fly north to the western Arctic, south to the South Pacific, east to the Atlantic, north to Greenland, and return to California across central North America. ATom establishes a single, contiguous, global-scale dataset. This comprehensive dataset will be used to improve the representation of chemically reactive gases and short-lived climate forcers in global models of atmospheric chemistry and climate.