Blood gas analyzers are able to provide information on a wide range of oxygenation parameters. Some of these data are complex. Their biological significance or clinical consistency are not always well known. This article aims to define these parameters, their reference values according to the type of sample; and to outline the possible errors during their interpretation. Thus, these reliable results can be integrated into the diagnostic procedure. We will see that the information provided by physicians plays an important role in their interpretation (temperature, patient ventilation condition, type of sample…). Knowing the physiological significance of complex data such as the oxygen alveolar-arterial gradient, or the estimated fraction of shunt, as well as the factors influencing them, allows us to improve their biological validation as accurately as possible. Finally, we will summarize the major oxygenation disorders and their impact on the results of blood gas analysis.