The interactions between gaseous sulfur dioxide and nickel oxide at 250°C have been investigated by means of temperature-programmed desorption (TPD) and microcalorimetric techniques. Depending on the thermal treatment of the oxide, different NiO samples were prepared containing chemisorbed oxygen species, O¹, O², O³ and O⁴, with different energies. The calorimetric data indicated that the weakly-bound species O¹ is the most reactive of the oxygen forms towards sulfur dioxide. In this case, the TPD curves (m/e=48 and m/e=32) show a new peak at 710°C; this may be correlated with the desorption of a sulfur-containing compound, probably NiSO₄, created by oxidation of sulfur according to the reaction S^IV ↔ S^VI. The regeneration of the species O¹ has been studied as a function of the temperature of oxygen adsorption; the most favourable temperature for the sulfation of nickel oxide appears to be about 400°C.