We document variability in O2, AOU, and heat content in the top 100 m of the world ocean (70¿S--70¿N) between 1955 and 1998 using observational data. The lowest O2 (highest AOU) content in the late-1950s are followed by high content in the mid-1980s and by low content in the late-1990s. The O2 and AOU content variability is characterized by relatively small linear trends superimposed on large decadal-scale fluctuations. The largest O2 content changes occur in the Northern Hemisphere (NH). The NH exhibits a negative linear trend in O2 content of ~-30 Tmol per decade between 1983 and 1998 and a positive linear trend of ~6 Tmol per decade between 1955 and 1998 (1 Tmol = 1012 mol). The trends in O2, AOU, and heat content are sensitive to the time frame of the measurements. The results indicate that a constant upper-ocean O2 content inventory should not be assumed on decadal time-scales.