OI Registration Code History

OI series of older UK registration numbers

The OI registration code forms part of the historic UK vehicle registration system used before the introduction of modern number plates. This code was originally associated with Belfast (B).

The information on this page records known registration series connected with the OI area code, together with their approximate issue dates where these are known. Most of the information relates to registrations issued between 1900 and 1972, meaning vehicles registered later may not necessarily appear in these records.

Historic registration codes are particularly useful when researching classic cars, motorcycles, commercial vehicles and other vintage vehicles. They can also help date old photographs, films and log books, or assist owners looking for a suitable age-related replacement registration.

OI registrations from Belfast (B)

The OI code was allocated to the Belfast (B) area. Before computerised registration systems, these letter combinations identified the local licensing authority responsible for issuing the number.

Many post-war registrations used three-letter combinations. In these cases, the second and third letters frequently represented the local area code. Vehicles carrying registrations containing OI therefore have a historic connection with Belfast (B).

Earlier vehicles carrying two-letter registrations using OI would also have been issued within this area.

OI registrations - Belfast (B)

Listed below are the known registration series associated with the OI code, together with the year letters and issue periods where these have been identified. Some codes were reused during different periods of the twentieth century, making the dates an important part of identifying a vehicle's age.

Example OI registration formats

Vehicles registered in this area could appear in a variety of formats depending on the period in which they were first registered. Examples of registrations incorporating the OI code are shown below.

These examples are provided purely to demonstrate historic registration formats and do not indicate that these registrations are currently available.

Learn More About UK Number Plate History

The OI series formed part of the wider history of British vehicle registrations. Over the years, registration formats evolved from early dateless numbers through to suffix plates, prefix plates and the current style system introduced in 2001.

You can explore the complete timeline of UK number plates, including when each format was introduced and how the registration system developed over more than a century.