Process for the carbonylation of a conjugated diene by reacting the conjugated diene with carbon monoxide and an hydroxyl group containing compound in the presence of a catalyst system based on: (a) a source of palladium cations, (b) a diphosphine ligand, and (c) a source of anions, wherein the diphosphine ligand is a ligand having the general formula I wherein x1 and x2 represent a cyclic group with at least 5 ring atoms, of which one is a phosphorus atom, and R represents a bivalent aliphatic bridging group, connecting both phosphorus atoms, containing from 2 to 4 atoms in the bridge, which is substituted with at least one substituent or R represents a phenyl group with both phosphorus groups bound to the 1,2-position.