Co catalysts that have been used in conversion of CO, H2, and olefins to carbonylic products can be regenerated by contact with an O2-N2 mixture at 100°-400° F. for at least 4 hr. The O2-N2 mixture has a composition of 1-25% O2 and 75-99% N2. Air makes a good regenerating gas. The regeneration may be done in situ. 4 United States patents cited.