A quantitative determination of proton contents in various chemically delithiated oxide cathodes has been carried out with prompt gamma-ray activation analysis (PGAA), and the results are complemented by mass spectrometric and thermogravimetric analysis data. While the delithiated layered Li1-xCoO2, Li1-xNi1/3Mn1/3Co1/3O2, and Li1-xNi1/2Mn1/2O2 show a significant amount of proton in the lattice at deep lithium extraction, orthorhombic Li1-xMnO2, spinel Li1-xMn2O4, and olivine Li1-xFePO4 do not encounter such proton insertion. Interestingly, spinel Li1-xCo2O4 shows both proton insertion and oxygen loss at deep lithium extraction. The differences are attributed to the differences in the chemical instability of the various cathodes. (c) 2006 The Electrochemical Society.