MEPC.2/Circular: provisional categorization of liquid substances

The MEPC.2/Circular, formally titled the provisional categorization of liquid substances in accordance with MARPOL Annex II and the IBC Code, is the annual IMO circular that records provisional assessments agreed under Annex II regulation 6.3. It is issued each December and each edition replaces all previously issued circulars under that title; the current edition is MEPC.2/Circ.31, dated 1 December 2025.

It carries twelve annexes. List 1 covers pure and technically pure products and mixtures assessed as a whole; list 2 pollutant-only mixtures whose components are already assessed; list 3 trade-named mixtures presenting safety hazards; list 4 pollutant-only mixtures with unassessed components; list 5 substances used only as components in trade-named mixtures. The remaining annexes carry vegetable oil synonyms, country codes, tripartite contact addresses, authorized manufacturers, cargo tank cleaning additives, biofuels and energy-rich fuels subject to MARPOL Annex I.

A provisional entry has a life. Under the guidelines at MEPC.1/Circ.512/Rev.1 of 15 October 2019, a tripartite agreement runs three years and then expires permanently, and no new agreement may be made for the same product, which is why each list 1 entry resting on one carries an explicit expiry date. The circular is not a cargo compatibility chart, a misdescription that recurs; compatibility is 46 CFR part 150. The full article will cover the assessment route through the GESAMP working group and the ESPH technical group.