The cyclopropene acid groups in cottonseed oil can be modified by a light hydrogenation which will not produce large amounts of trans isomers or lower the iodine value to a significant extent. Optimum eonditions, as indicated by this investigation, are 105-115C, 20 psig hydrogen pressure, 0.1% electrolytic nickel as catalyst, and a low hydrogen-dispersion rate.Under milder conditions of hydrogenation the elimination of the cyclopropenes was accompanied by a lower formation of trans isomers and a lower hydrogenation of noneyelopropenes, but the time required increased.In one hydrogenation carried out with commercial nickel catalyst, the 0.4% of malvalic acid groups in the cottonseed oil was hydrogenated completely whereas the iodine value was reduced by only 1.7 units and only 2.1% of trans isomers was formed.Winterization of cottonseed oils which had been hydrogenated to the point of eliminating their response to the Halphen test and in which only small amounts of saturated acid groups and tra~s isomers had been formed gave yields equal to or better than those of the original oil. Hydrogenation actually increased the ease of winterization.