A chiral alkanoic acid was prepared with up to 52% excess of the (S) enantiomer by hydrogenating alpha,beta-unsaturated carboxylic acid with a cinchonidine-Pd/Al2O3 catalyst system. Favourable conditions are : high surface hydrogen concentration (greater than or equal to 60 bar hydrogen pressure, low catalyst concentration and apolar solvents), near ambient temperature and a cinchonidine/reactant molar ratio of at least 0.4 mol%. It is proposed that high hydrogen solubility and the presence of 2-methyl-2-pentenoic acid reactant as dimers are advantageous for enantiodifferentiation.