Three series of cerium-promoted nickel—alumina catalysts with different nickel-to-aluminium ratios each containing different amounts of cerium have been prepared and characterized. The calcination and reduction behaviour were found not to be altered by the presence of cerium. Part of the promoter was found to separate during the precipitation process as poorly crystalline CeO2, the amount of which was largely determined by the drying temperature. This phase separation process was accompanied by a partial change in the valence state of the cerium. The effect of cerium on the nickel particle sizes was very small. Cerium enhances the activity of coprecipitated nickel—alumina catalysts in the carbon monoxide methanation reaction. This enhancement is accompanied by an increased apparent activation energy. Cerium- and lanthanum-promoted materials are compared with one another and it is concluded that although both promoters behave differently in determining the catalyst structure, their behaviour in the carbon monoxide methanation reaction is very similar and the specific activities of both types of material are nearly equal.