The CO2 reforming of CH4 over reduced NiO/alkaline earth metal oxide catalysts was investigated. A CO yield of 95% was obtained from a stoichiometric feed mixture of CH4 and CO2, at high GHSV (60 000 cm(3) g(-1) h(-1)), over a reduced NiO/MgO with a weight ratio of 0.2. In addition, the catalyst had excellent stability, since the CO yield remained unchanged during 120 h. Compared to the reduced NiO/MgO catalyst, the reduced NiO/CaO, NiO/SrO and NiO/BaO catalysts had low CO yields and very low stabilities. The TPD of CO over the reduced NiO/MgO catalyst indicated a lower decomposition of CO to CO2 than over the other catalysts investigated, hence that MgO inhibits the disproportionation reaction 2CO --> C + CO2 over Ni. The behavior of the reduced NiO/MgO catalyst is probably due to the formation of a NiO-MgO solution, as a result of the similar crystalline structures of NiO and MgO.