Provided is a selective hydrogenation process for producing aminonitriles by contacting the corresponding dinitriles with a hydrogen-containing fluid in the presence of a hydrogenation catalyst, a solvent and an additive for improving the yield of and/or selectivity to the aminonitrile. The additive comprises a carbon monoxide; a tetraalkylammonium hydroxide compound; a tetraalkylphosphonium hydroxide compound; a multi-centered metal carbonyl cluster; an organic isonitrile; a cyanide compound having at least one cyano group bound to other than a carbon atom; and afluoride compound.