IMO resolution numbering: how to read MEPC.391(81)

An IMO resolution designation carries two numbers and a body. In MEPC.391(81), MEPC is the Marine Environment Protection Committee, 391 is the sequential resolution number in that committee’s series, and (81) is the session at which it was adopted. The same convention runs across MSC.NNN(SS) for the Maritime Safety Committee and A.NNN(SS) for the Assembly. The two numbers advance independently, so a resolution number cannot be inferred from a session or the reverse.

That structure is why a wrong session number is a silent error rather than an obvious one. MEPC.391(82) is well formed, sounds plausible, and names a resolution that does not exist: the MEPC 82 series ends at MEPC.396(82) and MEPC.391 belongs to MEPC 81, adopted 22 March 2024. The check is mechanical. The resolution index serves every MEPC resolution at a path keyed by its designation, so a designation that 404s there is a designation to distrust.

The full article will cover the committee and Assembly series and their prefixes, the circular series (MEPC.1/Circ, MSC.1/Circ, MSC-MEPC joint circulars) and how they differ in status from a resolution, the distinction between a resolution that adopts a MARPOL or SOLAS amendment and one that issues recommendatory guidelines, why an approved draft carries no resolution number until adoption, and the verification routine: designation to index path, index path to served document, served document to the identifier printed on its own cover.