Abstract: Olefinically unsaturated compounds are hydroformylated continuously, the olefin being passed into the lower region of the reactor, under from 1 to 40 bar and at from 50.degree. to 140.degree. C. with the aid of a rhodium complex as a catalyst in a hydroformylation reactor having a liquid reaction zone which occupies about 60-85% of the reactor volume, the gaseous products and reactants being removed from the hydroformylation reactor, the products being isolated and the major part of the remaining gas being recycled to the reactor by the cycle gas method, by a process in which from 20 to 80% by volume of the cycle gas is fed into the hydroformylation reactor above the liquid reaction zone and/or below the liquid surface in the top fourth of the liquid reaction zone.