A method of controlling a hydroformylation process for producing normal (N) and iso (I) aldehydes at a N:I ratio, the process comprising contacting an olefinically unsaturated compound, e.g., propylene, with synthesis gas and a catalyst comprising a transition metal, e.g., rhodium, and an organopolyphosphite and an organomonophosphite ligand, the contacting conducted at hydroformylation conditions comprising a synthesis gas partial pressure, the method comprising increasing the synthesis gas partial pressure in the first reaction zone to decrease the N:I ratio or decreasing the synthesis gas partial pressure in the first reaction zone to increase the N:I ratio.