Alkenols are made from the corresponding olefines by passing a gaseous mixture comprising olefine and oxygen at 150 DEG to 600 DEG C., a pressure of 1.0 to 15 atmospheres and a space velocity of 500 to 4000 v./v./hour in contact with a catalyst comprising oxidized Cu, Mo and Cr on a refractory support, the catalyst being 1 to 20% of the support and the ratio of ingredients being Cu : Mo : Cr 1 : 0.05 to 2.0 : 0.05 to 2.0. If desired steam may be incorporated in the reactant gaseous mixture. Propylene or isobutylene may be oxidized to acrolein or methacrolein respectively. Typical exit gas mixtures from a reactor contain unreacted olefine, e.g. isobutylene, other carboxylic components, acids, carbon dioxide and carbon monoxide.ALSO:Oxidation catalysts comprise oxidised Cu, Mo and Cr on a refractory support, the catalyst being 1-20% of the support and the ratio of ingredients being Cu:Mo:Cr 1:0.05 to 2.0:0.05 to 2.0. The catalyst may be prepared from an aqueous ammoniacal solution of a copper halide, a molybdate and a chromate, by imprgenating a refractory material therewith, drying and activating at 400-500 DEG C. for 5-25 hours. Specified refractory materials are Al2O3, SiO2, pumice, and SiC.