IMO company numbers: the seven digits that are not a ship

There are two IMO numbering schemes, not one. The ship identification number has been attached to hulls since 1987, seven digits that outlive every rename, reflag and sale. The company and registered owner identification number does the same job for the businesses behind the ship: the owner, the registered owner, the manager. It is also seven digits.

They appear in the same field. On the EU’s consolidated financial sanctions file, an identification element of type imo sits on a record exactly the way a passport number sits on a person. Nothing in the field name, the format or the surrounding structure says which scheme the number belongs to.

What goes wrong

A tracker that reads every IMO-typed number as a hull will publish companies as ships. The record carries a plausible name, a listing date, a legal basis and a link to the regulation, so the resulting page looks exactly like a vessel page. It has a designation and a source. It simply is not a ship.

This happened here on 7 September 2026. The EU’s financial sanctions file returned to service after an outage, our parser read its imo identifications as hull numbers, and five shipping companies — Lukoil-Marinbunker among them — appeared in the vessel directory for about nine minutes before the next run removed them. Every one of the forty-one such records in that file belongs to a company.

We no longer read that file at all. From 2 October 2026 its public download redirects to an EU Login sign-in page, and since it never held a vessel, the only thing lost was a set of company records. The lesson stands for any list that does carry both kinds of record.

The failure is quiet, which is what makes it worth writing down. Nothing errors. The count goes up rather than down, so a plausibility check on the fleet size passes. The only signal is the check digit, and only if you test it.

The check digit

An IMO ship number’s last digit is a checksum: multiply the first six digits by 7, 6, 5, 4, 3 and 2, sum the products, and the final digit of that sum is the seventh digit. Company numbers are issued from a different scheme and carry no such relationship, so most of them fail the test.

Of the forty-one company numbers in that EU file, thirty-eight failed it outright. Three passed by coincidence — one number in ten will — which is the whole lesson: the check digit is a filter, not a proof. Something has to look at what the record claims to be.

What this site does

Three rules, in order:

1. Reject anything failing the check digit. It is never looked up, and the bulk screener says why rather than returning “no record”, because those two answers mean completely different things to somebody checking a counterparty.
2. Read the record, not just the field. In the EU file a record becomes a vessel only when its narrative opens by naming a ship. An identification of type imo on a company record is treated as what it is — the company’s number — and carried on the company, where it is genuinely useful for matching an owner across lists.
3. Publish the number anyway. Company numbers are not noise. They are the most reliable way to tell one “Ocean Shipping Ltd” from another, and they appear on company pages for that reason.

The same trap sits in the UN consolidated list, whose seven-digit identifiers are largely company numbers too. Any list that names shipping companies will contain them. The question is never whether the number is real — it is which of the two schemes it belongs to.

If you are building something

Test the check digit before you join on the number. Keep company identifiers in a separate column from hull identifiers, even when the source puts them in one. And when a number fails, say so out loud instead of dropping the row: a screening result that quietly loses a line is worse than one that admits it could not read it.

The API applies all of this. A request for a vessel whose IMO number fails the check digit returns check_digit_failed with an explanation, never an empty result.