Increasing the propylene content of the propylene feed delivered to a continuous hydroformylation process from the 95 mole % maximum level that is usual in typical chemical grade propylene to at least 97 mole %, for example to the 97.5% level obtainable from the conversion of oxygenates to olefins or the 99.5% level of polymer grade propylene, enables adjustments to be made in the syngas feed to the process. This leads to surprising improvements in hydroformylation product yield, in reactor capacity utilization and in the reduction of amounts of waste gases.