A continuous hydroformylation process for producing a mixture of aldehydes with improved flexibility and stability of a normal/branched (N/I) isomer ratio of the product aldehydes. The process involves reacting one or more olefinically-unsaturated compounds with carbon monoxide and hydrogen in the presence of an organopolyphosphite ligand and an organomonophosphite ligand, at least one of such ligands being bonded to a transition metal to form a transition metal-ligand complex hydroformylation catalyst; the process being conducted at a sub-stoichiometric molar ratio of organopolyphosphite ligand to transition metal, at a super-stoichiometric (>2/1) molar ratio of organomonophosphite ligand to transition metal, and at a carbon monoxide partial pressure in the inverse order region of the hydroformylation rate curve; and controlling and varying the isomer ratio by varying the concentration of organopolyphosphite ligand relative to transition metal.