The instability of the electrolyte and the sluggish kinetics of the reactions hinder the application of Li-O-2 batteries. In this study, we aim to better understand the behavior of oxygen reduction (ORR) and evolution (OER) reactions in dimethyl sulfoxide (DMSO), Tetraglyme (G4) and their blend DMSO-G4, with emphasis on the role of solvent nature in the mechanism and reaction route, using rotating ring-disc electrode (RRDE) and differential electrochemical mass spectrometry (DEMS). Interestingly, RRDE results showed that the stability and the ratio of the formed O-2(-.) : Li2O2 increase with addition of DMSO to G4. A proposed mechanism for ORR is discussed. Depending on the solvation ability of the solvent, which primarily determines the lifetime and solubility of the superoxide intermediate in solution, a solution or a surface-based pathway is followed: in highly solvating solvents (e.g. those with high donor or acceptor number) such as DMSO, superoxide is stabilized in solution; while in low solvating solvent, it is further reduced to Li2O2, blocking the surface. The results of the scan rate variation under defined mass transport in DMSO suggest a sequential formation of monolayers of Li2O2 during reduction. In G4-solutions, despite of the reversible formation of Li2O2, deactivation of the electrode takes place, as evidenced by DEMS. This could arise from a reduction products-induced decomposition of the electrolyte, forming a deactivating film on the surface during ORR, which is only partially removed at higher potentials evolving CO2. Also, we found that DMSO is more active towards OER than G4. The electrode material as well influences the kinetics, in particular of OER. These findings could have implications for the development of Li-air battery. (C) 2017 Elsevier Ltd. All rights reserved.