O-2-release from carbon-bearing Ni(II) ferrite (CBNF) was studied with TG-MS and DSC. Release of lattice oxygen as O-2 was found to take place at 200-300 degrees C and was associated with an endothermic temperature peak. The proposed thermochemical reaction is O-lat(s) = V-o(s) + (1/2) O-2(g),Delta H degrees = 424.5 kJ/mol, where O-lat(s) and V-o(s) denote the lattice oxygen of CBNF and the oxygen-deficient site on the surface of the CBNF. At a temperature higher than 350 degrees C, lattice oxygen was released as CO2 and was accompanied by a decrease of deposited carbon.