Tacit acceptance: how IMO amendments enter into force

Tacit acceptance is the mechanism that lets an IMO convention be amended without waiting for each party to ratify. Under MARPOL article 16 and the equivalent SOLAS article VIII, an amendment adopted by the relevant committee is deemed accepted on a stated date unless a specified proportion of parties objects before it, and it enters into force a further stated interval after that. The clock is the reason amendment dates come in threes: adoption, deemed acceptance, entry into force.

The sequence starts at adoption, and nothing before adoption starts it. A committee that approves a draft has taken a procedural step only: the draft carries no resolution number, no deemed-acceptance date and no entry-into-force date. The IMO Net-Zero Framework is the working example. MEPC 83 approved a draft revised MARPOL Annex VI on 11 April 2025, the extraordinary session MEPC/ES.2 of 14 to 17 October 2025 adjourned without adopting it, and every entry-into-force date published before that adjournment was counted from an adoption that has not happened.

The full article will set out the article 16 and article VIII texts side by side, the objection thresholds and who may object, the standard intervals and where they differ between instruments, the practical effect of the survey-date rather than calendar-date application that many amendments use, how a flag state records an objection, and the distinction between an amendment in force and one applicable to a given ship.