An improved process for the preparation of alkyl formylvalerates, wherein butadiene or a butadiene-containing hydrocarbon mixture is reacted, in a first stage, with carbon monoxide and alkanols in the presence of cobalt carbonyl complexes and, per mole of butadiene, from 0.5 to 2 moles of tertiary nitrogen bases having a pK.sub.a of from 3 to 11, at from 80.degree. to 150.degree. C. and from 300 to 2,000 bar, and, in a second stage, the resulting alkyl pentenoate is reacted with carbon monoxide and hydrogen in the presence of cobalt carbonyl complexes at from 100.degree. to 160.degree. C. and from 100 to 300 bar, the improvement being that tertiary nitrogen bases, excess alkanols and any unconverted hydrocarbons are distilled off from the reaction mixture obtained in the first stage, with the proviso that the reaction mixture is treated, before or during the distillation, with gases containing molecular oxygen, and the residual reaction mixture containing alkyl pentenoate and cobalt catalyst is used in the second stage.