A systematic study of the hydroxycarbonylation reaction of styrene is described. The effect of the catalytic precursor and the reaction conditions on the results of the reaction was investigated. Several monophosphines (PPh3, P(p-Tol)(3), P(p-C6H4OMe)(3), P(p-C6H4F)(3), PPh2(o-Tol), PMe3, PCy3) and diphosphines (dppe, dppp, dppb, dppf, HomoXantphos, DPEphos, Xantphos, BDPP, BINAP, BPPFA, DIOP) were applied to control the regioselectivity of the reaction. The effect of the bite angle of the diphosphines has also been studied. Catalysts containing monophosphines as ligands give 2-phenylpropanoic acid as the major product and the 3-phenyl propanoic acid is obtained when diphosphines are used. Two catalytic cycles are proposed to explain the influence of the different palladium precursors with mono- and diphosphines.