Abstract: It has been discovered that, whereas magnesium oxide of commerce, usually made by roasting hydrated magnesia, is inert to the action of CO.sub.2 and methanol, when the oxide is made by roasting magnesium carbonate at a critical temperature in the range of 600.degree.-1200.degree. F., it dissolves rapidly in anhydrous methanol under CO.sub.2 pressure, to form a methylate-carbonate. The complex can be emulsified with lubricating oil in the presence of an oil soluble surface active agent, particularly magnesium mahogany sulfonate, to produce an additive for lubricating oil having a high alkali value in the range of 100-400 mg. KOH per gram.