A hydroformylation system for making aldehyde by reacting olefin with synthesis gas by way of hydroformylation is improved by multi-stage condensation of gaseous reactor effluent for providing liquid feed to a gas-liquid contact zone. The process provides for condensing and separating the gaseous reactor output stream in a plurality of successive condenser stages into gaseous condenser output streams and liquid condenser output streams having differing temperatures and feeding the recovered liquid to the gas-liquid contact zone to improve olefin recovery by stripping.