The present invention relates to a family of carbohydrate monosulphate fatty acid esters, which contain less than 10 mole % of carbohydrate polysulphate fatty acid esters, and to a method of preparation thereof. The monosulphate carbohydrate esters according to the invention comprise one sulphate ester and at least one fatty acid and are among others useful as adjuvants for immunological products such as vaccines.