SUMMARYWithin the global oil shipping sector, flag states that inadequately fulfil obligations to effectively exert jurisdiction over vessels flying their flags have been criticized for facilitating the existence of substandard ships. This paper examines the topic of flag-use and its potential association with oil spill risk. Flags most associated with accidental oil spills were identified through comparing the flag composition of the global oil tanker fleet with that of vessels that have been involved in the 100 largest tanker spills on record. Vessels flying flags of states that have exhibited consistent patterns of failure in compliance with international obligations, defined here as ‘flags of non-compliance’ (FoNCs), were found to be significantly more common amongst the vessels that have been involved in spill incidents. However, this was dependent on how the Liberian flag was qualified throughout the time period considered. If measures are being sought to reduce the risk of tanker involvement in large-scale oil spills further, vessel owners should be deterred from registering with FoNCs that are highly accessible to foreign owners, and political measures should be taken to put pressure on flag states that operate all other FoNCs to improve effective jurisdiction over ships flying these flags.