About 19 000 African Penguins (Spheniscus demersus) were oiled when the bulk ore carrier MV Treasure sank off the west coast of South Africa in June 2000. Of these, more than 17 000 Penguins were cleaned, rehabilitated and released back to the wild. The breeding success of these birds was compared with unoiled birds and birds oiled during other oil-spills, by measuring fecundity, hatching success and fledging success from 2001 to 2005 on Robben Island. Fledging success averaged 61% in birds that were not oiled in the Treasure spill and 43% in birds oiled during the Treasure event, with a large proportion of the reduction attributable to higher mortality of older chicks. Factors that may have contributed to differential fledging success include long mean intervals between capture and cleaning (22 days) and between capture and release (48 days) for birds oiled in the Treasure spill. One implication of these results is, if a similar large spill should occur in the future, every effort should be made to treat the oiled birds as quickly as possible to reduce the risk of their suffering a similar reduction in breeding productivity. Further, the other interventions, such as relocation of unoiled birds and captive-rearing of orphaned chicks may need to receive higher priority than hitherto.