Port state control (PSC) is the system of inspections that countries perform on foreign-flagged vessels visiting their ports. The premise is that international maritime regulation can only be enforced effectively at the point of arrival, by countries other than the flag state, because flag-state oversight is inconsistent. PSC has been the dominant compliance enforcement mechanism in commercial shipping since the 1980s.
Regional MoUs
PSC is organised through regional Memoranda of Understanding (MoUs). The Paris MoU covers Europe and the North Atlantic; the Tokyo MoU covers the Asia-Pacific; the Viña del Mar Agreement covers Latin America; the Caribbean MoU covers the Caribbean basin; the Mediterranean, Indian Ocean, Black Sea, Riyadh, Abuja and Persian Gulf MoUs cover their respective regions. The United States Coast Guard runs its own PSC programme under domestic law. The MoUs share data and coordinate inspection priorities through a global PSC database.
What PSC inspectors look at
PSC inspectors check certificates (SOLAS, MARPOL, MLC, ISM, ISPS), structural condition, lifesaving and firefighting equipment, working and living conditions for the crew, and compliance with the most recent IMO conventions. They have authority to detain vessels with serious deficiencies until the deficiencies are rectified.
Targeting and white/grey/black flags
Each MoU publishes performance-based lists ranking flag states from white (best) through grey to black (worst) based on detention rates. Vessels flagged with black-list states are inspected more frequently than vessels flagged with white-list states. The same logic applies to recognised organisations (classification societies) and to individual ship operators with poor records.
Why this matters for vessel research
Detention records are public. If a vessel has been detained by PSC, the detention notice is published by the relevant MoU and is visible in commercial databases such as Equasis. When researching the operational history of a particular vessel — for due diligence, journalism, or insurance — the PSC detention record is one of the more useful indicators of risk.