Kinetic adsorption of the different oxygen species on nickel oxide has been studied in the temperature range 250-750°C by means of a temperature-programmed desorption technique and a microcalorimetric method. Among the six oxygen forms enumerated, it is possible to distinguish two kinds of species, each one being characterized by the value of its enthalpy of adsorption: ΔH₁=-14.3 kcal mol^-1 for class 1; ΔH₂=-115.5 kcal mol^-1 for class 2.