In order to investigate the nature of Ni supported on ␣-Al 2 O 3 and its modification with Sn in methane reforming reactions, a theoretical study was carried out. A molecular orbital approach of the extended Hückel type was performed to obtain the formation energies of postulated adsorbed and reacted species of CH 4 , H 2 O, O 2 and CO 2 on a model of Ni and NiSn surfaces resembling Ni/␣-Al 2 O 3 and NiSn/␣-Al 2 O 3 . Three different known planes of fcc Ni were considered: (1 1 1), (0 0 1) and (1 1 0). Possible adsorbed and reacted species of CH 4 , H 2 O, O 2 and CO 2 on Ni with Ni all around, Sn fully rounded by Ni and Ni near a Sn were discussed using reaction energies. The interaction NiSn in Ni clusters has been claimed to be of interstitial substitution-type in alloys. The (1 1 1) plane is the most reactive for adsorption. In agreement with experimental work, methane activation on Ni is the controlling step in reforming of methane with CO 2 (R), partial oxidation with O 2 (POM) and mixed reforming using CO 2 and O 2 (MR). Sn near a Ni changed the adsorption properties of it. Favoured reactions for Sn rounded by Ni on (0 0 1) and (1 1 1) planes are the adsorption of CO 2 and formation of a Sn-CO bond and the generation of Sn-H bonds from methane and water dissociation. The theoretical results are discussed in the context of previously published experimental data.