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IMO identification number scheme


(Circular letter No.1886/Rev.5)

The IMO ship identification number scheme was introduced in 1987 through adoption of resolution A.600(15), as a measure aimed at enhancing "maritime safety, and pollution prevention and to facilitate the prevention of maritime fraud". It aimed at assigning a permanent number to each ship for identification purposes. That number would remain unchanged upon transfer of the ship to other flag(s) and would be inserted in the ship's certificates. When made mandatory, through SOLAS regulation XI/3 (adopted in 1994), specific criteria of passenger ships of 100 gross tonnage and upwards and all cargo ships of 300 gross tonnage and upwards were agreed.

The implementation of the scheme became mandatory for all ships as of 1 January 1996.

In December 2002, the Diplomatic Conference on Maritime Security adopted a number of measures aimed at enhancing security of ships and port facilities. This included a modification to SOLAS Regulation XI-1/3 to require ships' identification numbers to be permanently marked in a visible place either on the ship's hull or superstructure. Passenger ships should carry the marking on a horizontal surface visible from the air. Ships should also be marked with their ID numbers internally.

The IMO ship identification number is made of the three letters "IMO" followed by the seven-digit number assigned to all ships by IHS Maritime (formerly known as Lloyd's Register-Fairplay) when constructed. This is a unique seven digit number that is assigned to propelled, sea-going merchant ships of 100 GT and above upon keel laying with the exception of the following:

  • Vessels solely engaged in fishing
  • Ships without mechanical means of propulsion
  • Pleasure yachts
  • Ships engaged on special service (e.g. lightships, SAR vessels)
  • Hopper barges
  • Hydrofoils, air cushion vehicles
  • Floating docks and structures classified in a similar manner
  • Ships of war and troopships
  • Wooden ships

This number is assigned to the total portion of the hull enclosing the machinery space and is the determining factor should additional sections be added.

The IMO number is never reassigned to another vessel and is shown on the ship’s certificates.


IMO ship identification number - contact

IHS Maritime is the sole authority for identifying and assigning an IMO number.
For verification of IMO numbers for individual ships, IHS Maritime operates a service following receipt of a completed IMO number Request Form.

IHS Maritime
(Part of IHS Global Limited)
Sentinel House
163 Brighton Road
Surrey CR5 2YH
United Kingdom

International telephone: (+44) (0)1737 379054
International fax: (+44) (0)1737 379040 
(Circular letter No.2554/Rev.3)
The IMO Unique Company and Registered Owner Identification Number Scheme was introduced through the adoption by the Maritime Safety Committee (MSC), at its seventy-eighth session (12 to 21 May 2004), of resolution MSC.160(78), as a measure to enhance maritime safety, security and environmental protection, and to facilitate the prevention of maritime fraud.  Its purpose is to assign a permanent number for identification purposes to each company and/or registered owner managing ships of 100 gross tonnage and above engaged on international voyages.  Additionally, Administrations are invited to participate in the scheme to the extent they desire by assigning an IMO unique company and registered owner identification number (hereinafter, referred to as “Number”) to each company and/or registered owner managing ships of 100 gross tonnage and above not engaged on international voyages.  The procedures for the implementation of resolution MSC.160(78) were initially circulated by means of Circular letter No.2554, dated 24 June 2004.
The Committee, at its eightieth session (11 to 20 May 2005), adopted the proposed new SOLAS regulation XI‑1/3‑1 on the company and registered owner identification number and amendments to SOLAS regulation XI‑1/5 on the continuous synopsis record (resolution MSC.194(80)), which should be deemed to have been accepted on 1 July 2008 and should enter into force on 1 January 2009.
MSC 80 also adopted amendments to the International Management Code for the Safe Operation of Ships and for Pollution Prevention (ISM Code) (resolution MSC.195(80)) and to the International Code for the Security of Ships and of Port Facilities (International Ship and Port Facility Security (ISPS) Code) (resolution MSC.196(80)) introducing references to the company and registered owner identification number.
The IMO Unique Company and Registered Owner Identification Number Scheme is managed, in parallel with the IMO Ship Identification Number Scheme (resolution A.600(15)) and procedures for the implementation thereof (Circular letter No.1886/Rev.5), without charge by IHS Maritime.  The scheme may assign Numbers to companies and/or registered owners of ships not required to have IMO ship identification numbers.
The Number is a IHS Maritime number, allocated at the time of issuance of the documents detailed in paragraph 6 of the Annex to resolution MSC.160(78) or registration of a ship not required to have these documents. The Number consists of seven digits assigned by IHS Maritime. The label begins with the letters "IMO" followed by either "Company" or "Registered Owner", then, followed by the seven digits.
Once assigned, the Number remains unchanged for a company and/or registered owner. When companies and/or registered owners merge, as a matter of general policy, IHS Maritime assigns the Number of the larger company and/or registered owner to the new amalgamated entity, while the Number of the smaller entity is frozen and not re-used.
The methods for obtaining Numbers on existing registered owners and companies, for assigning a Number to registered owners or companies that have not previously been assigned a Number and for communicating corrected company details on existing records, on an individual basis, are as follows:
-   a free website ( which allows registered users to look up Numbers, by using the available “Search” facility.  When the companies or registered owners cannot be identified through the “Search” function, authorized data providers should request the assignment of new Numbers or provide corrective information on existing records. The website has a free user registration system to enhance both the security of the site and the information;
-  paper request forms; and
-  a free web service for Administrations to facilitate the provision of individual company and registered owner data from IHS Maritime to flag Administrations in an electronic format for ship registration purposes.
IMO unique Company and Registered Owner identification number - contact
IHS Maritime
(Part of IHS Global Limited)
Sentinel House
163 Brighton Road
Surrey CR5 2YH
United Kingdom

International tel.:       (+44) (0)1737 379054
International fax:       (+44) (0)1737 379040 

The Numbers are also available on the free public website of Equasis (