Mg-O-2 batteries appear to be a promising alternative to Li-O-2 system due to the high abundancy and volumetric energy density of Mg. Although much effort has been put into research on Li-O-2 batteries, little is known about the oxygen reduction and evolution in Mg2+-containing aprotic electrolytes. In this paper, we present a detailed analysis of the ORR in Mg2+-containing DMSO using RRDE and DEMS-techniques and derive a more general reaction mechanism of ORR in aprotic electrolytes using the results for Li+, Na+ and K+-containing DMSO. O-2 first reacts via an initial adsorption step to superoxide which, in the presence of Mg2+, is subsequently reduced to peroxide as the main reaction product. However, this product undergoes further reactions leading to a deactivation of the electrode. Regarding the reversibility, unfortunately no OER was observed and reactivation of the electrode proved difficult. (C) 2016 Elsevier Ltd. All rights reserved.