The invention relates to a process for the continuous preparation of aldehydes and/or alcohols having at least 6 carbon atoms by multistage hydroformylation of olefins or olefin mixtures having at least 5 carbon atoms in the presence of unmodified cobalt complexes, in which at least two reactors are operated at different temperatures in the temperature range from 100 to 220° C. and pressures of from 100 to 400 bar, which is characterized in that a) one reactor is operated at temperatures above 160° C. by the one-pot process with simultaneous catalyst formation, catalyst extraction and hydroformylation and the amount of water fed into the reactor with the aqueous cobalt salt solution is greater than that discharged from the reactor with the liquid reaction mixture and the gas phase together, with part of the aqueous bottom phase being discharged from the reactor to keep the level of the aqueous bottom phase constant, b) and the cobalt carbonyls in the aqueous phase taken off or part thereof are introduced into the reactor which is operated at a lower temperature.