Differential electrochemical mass spectrometry (DEMS) was used to study the electrochemical decomposition of organic carbonate electrolyte solutions at practical lithium metal oxide composite electrodes used in lithium-ion batteries. For propylene carbonate (PC), CO2 evolution was detected at LiNiO2, LiCoO2, and LiMn2O4 composite electrodes. The starting point of gas evolution was 4.2 V vs. Li/Li+ at LiNiO2, whereas at LiCoO2 and LiMn2O4, CO2 evolution was observed only above 4.8 V vs. Li/Li+. In addition, various other volatile electrolyte decomposition products of PC were detected when using LiCoO2, LiMn2O4, and carbon black electrodes. In ethylene carbonate/dimethylcarbonate, CO2 evolution was detected only at LiNiO2 electrodes, again starting at about 4.2 V vs. Li/Li+.