Copernicus Marine in situ TAC (CMEMS INSTAC) aggregates and provides to users a large panel of Biogeochemical (BGC) variables together with useful metadata information on the platforms. The main parameters available in the near real time (NRT) CMEMS INSTAC products are dissolved oxygen concentration, nutrients (nitrate, silicate and phosphate), chlorophyll, fluorescence and pH. The following document aims to give a detailed picture of the processes and tools used to validate BGC datasets found in the NRT CMEMS INSTAC products 030 to 036. Due to the recent nature of CMEMS INSTAC BGC quality control activity, the present document is focused on the dissolved oxygen concentration. It will be progressively updated with other BGC parameters. The NRT CMEMS INSTAC products integrate observation aggregated from the Regional EuroGOOS consortium (Arctic-ROOS, BOOS, NOOS, IBI-ROOS, MONGOOS) and Black Sea GOOS as well as from SeaDataNet2 National Data Centers (NODCs) and JCOMM global systems (Argo, GOSUD, OceanSITES, GTSPP, DBCP). Oxygen measurement is stored within its original unit only that depends either on the kind of sensor or chemical method used for measurement, or on the data provider. Dissolved oxygen concentration is thus available either in ml/l or in µmol/l or in µmol/kg. Quality control flags are positioned to inform the users of the level of confidence attached to the observations.