The surface reaction of SO@sub 2@ and O on a Ni (100) surface has been investigated using a Near Edge X-ray Absorption Fine Structure (NEXAFS) technique and X-ray Photoelectron Spectroscopy (XPS). Four different surfaces were studied; clean Ni(100), p(2x2)_O/Ni(100), c(2x2)_O/Ni(100), and NiO(111)/Ni(100). Chemisorbed SO@sub 2@ was formed at 160 K on all four surfaces. Upon heating, SO@sub 2@ was decomposed to SO and atomic sulfur on clean Ni(100). On p(2x2)_O/Ni(100) and c(2x2)_O/Ni(100), however, SO@sub 3@ was formed in the temperature range of 200 to 400 K. Sulfur K-edge NEXAFS results showed that SO@sub 3@ was adsorbed with C3-axis perpendicular to the surface. On the NiO(111)/Ni(100) surface, both SO@sub 3@ and SO@sub 4@ were formed.