The hydrogenation of olefins in acidic aqueous solutions was studied on platinum catalysts under potential control. This control was achieved by an external device or was spontaneously established in the presence of the reactants. It is found that the catalytic activity does not depend on the way of potential control, or on the source of hydrogen (gaseous hydrogen or reduced protons). This result implies the same mechanism in the case of catalytic and electrocatalytic hydrogenation of olefins. Moreover the same type of active hydrogen species is involved in these reactions, identified as a weakly bound one. In competitive hydrogenations of methyl substituted olefins, high selectivities can be obtained by control of the potential of the catalyst at rather positive values.