overbased mgo dispersions with high magnesium content and acceptably low viscosities are reproducibly prepared without gel formation by heating to 280 - 360 ° c . a mixture of mgo , selected dispersants , low mw carboxylic acids , water and a combination of high boiling hydrocarbon and organic diluent , wherein water is more than 8 %, typically more than 10 % of the reaction mixture . no additional solubilizing or dispersing agents , promoters or reactants such as carbon dioxide , amines , alcohols etc are needed to obtain the desired dispersions . compositions such as lubricating oils and fuels containing the overbased magnesium dispersions as additives are also disclosed .