The behavior of layered LiMO2 (M=transition metal) oxides has been investigated systematically as a function of composition for the oxygen evolution reaction (OER) in alkaline electrolytes. The rich variety of LiMO2 compositions with the O3-type layered structure makes this class of materials an excellent testbed for understanding the effects of the nature and oxidation states of the transition-metal ions on the OER. Accordingly, the OER behaviors of a range of LiMO2 oxide solid solutions are presented here: LiCo1−xMnxO2, LiNi1−xMnxO2, and LiCo1−xNixO2 with 0.25≤x≤ 0.7. It is found that the OER activity increases with decreasing Mn content, and the Ni-rich compositions exhibit high OER activities. Furthermore, the pre-OER potential region displays contributions from surface faradaic reactions that involve Ni and Co. The overall higher activity of the Ni- and Co-rich compositions might be due to the in situ transformation of the LiMO2 surface into a highly active electrocatalyst.