Dimethyl Sulfoxide (DMSO) was evaluated as a practical solvent for the rechargeable lithium air battery. Redox characteristics of the dissolved oxygen and its reduction products in the presence of lithium hexafluorophosphate (LiPF6) supporting electrolyte were studied via cyclic, rotating disk (RDE) and ring-disk (RRDE) electrode voltammetry. The DMSO medium facilitates reversible reduction and oxidation processes in contrast to other solvent-based electrolytes studied. Galvanostatic discharge-charge cycling of the Li-O-2 cells has shown characteristics of rechargeability expected from voltammetric studies. Multiple high-efficiency discharge-charge cycles are possible if the depth of discharge of the carbon cathode is limited to avoid excessive passivation by the discharge products. The discharge voltage of this Li-O-2 cell is higher than cells assembled with other non-aqueous organic electrolytes, an attribute ascribed to the stability of superoxide (O-2(-)), the one-electron reduction product of oxygen. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.048302jes] All rights reserved.