Lactones are prepared by the catalytic carbonylation of oxiranes using a catalyst system comprising a) at least one carbonylation catalyst A comprising uncharged or anionic transition metal complexes of metals of groups 5 to 11 of the Periodic Table, b) at least one metal compound B of the formula (I) MXxRn-x  (I)  where M is an element of group 2, 3, 4, 12, 13, R is hydrogen or a hydrocarbon radical which may be substituted on the carbon atoms other than on the carbon atom bound to M, X is an anion, n is a number corresponding to the valence of M, x is in the range from 0 to n, and c) at least one organic, chiral compound C which has fewer than four coordination sites.