Magnesium (Mg) alloys are becoming increasingly important in the biomedical field as temporary bone implants. However, the biodegradation process of Mg alloys is highly complex and recent findings suggest that oxygen (O-2) consumption is non-negligible. In this study, we give experimental proof of O-2 consumption during Mg degradation under physiological conditions. Specifically, we study pure Mg, Mg-6 wt%Ag and Mg-5 wt%Gd in Hanks' balanced salt solution and Dulbecco's modified Eagle's medium. We show that O-2 consumption and hydrogen evolution are inversely correlated and that O-2 concentrations remain below 7.5% in certain cases, which could have significant implications for bone healing.