A method of controlling an in-series, multiple, e.g., two, reaction zone, hydroformylation process for producing normal (N) and iso (I) aldehydes at a N:I ratio, the process comprising contacting an olefinically unsaturated compound with synthesis gas and a catalyst comprising (A) a transition metal, e.g., rhodium, (B) an organobisphosphite ligand, and (C) an organomonophosphite ligand, the contacting conducted in first and subsequent reaction zone(s) and at hydroformylation conditions comprising a transition metal concentration in each zone, the method comprising decreasing the transition metal concentration in the first reaction zone to decrease the N:I ratio or increasing the transition metal concentration in the first reaction zone to increase the N:I ratio.