Phases from the LiNixMnxCo1-2xO2 series (0≤x≤0.5) including NMC111 and NMC442 are considered as important layered cathode materials for lithium-ion batteries. The enthalpies of formation from oxides and oxygen and from elements of samples in this series with e.g. x = 0, 1/6, 1/3, 0.4, and 0.5, respectively, were determined using high temperature oxide melt drop solution calorimetry. We show that the investigated NMC phases are energetically more stable than LiCoO2. This is in agreement with better electrochemical cycling performance of Ni/Mn-rich compounds at higher voltages.