Hydrogenation is a reaction in which unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected.

The industrial application of hydrogenation is in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains, while animal fats have saturated carbon chains. This process converts unsaturated oils into saturated fats, and oils containing unsaturated fatty acids should be chosen for cooking.