At current rates that it would not need replacing at least until the end of the 21st century, but the expected lifetime of the series is stated as being forty-five years.

In 1992, the design was changed to one of black characters on a white background in metal or fibreglass; in that same year, the European blue ribbon was added with the Portuguese 'P' denominator.

Additionally, rather than the international road code 'P', these plates display a unique 'U' on the blue Euroband, joined by the EU flag on top.

The country was divided into zones (North, Centre, South, and, from 1918, the Azores and Madeira), each having an identification number sequence for the licence plates, which was N–000, C–000, S–000, A–000 and M–000 respectively.

By the mid-1930s so many vehicles had already been registered, especially in the South Zone (which included Lisbon), that the identification numbers have already reached five digits.

The sequencing by zones was maintained, with the letters AA to LZ reserved for the South (Lisbon), MA to TZ for the North (Oporto) and UA to ZZ for the Center (Coimbra).

The letters MG, and later, ME and MX were reserved for the Army, AP for the Navy, AM for the Air Force and EP for government ministries.

The letters TA, TB and TC, in red plates with white characters were reserved for temporary licences respectively in Lisbon, Oporto and Coimbra.

The white letters on red TD, TG, TH and TF were for temporary licences respectively in Ponta Delgada, Angra, Horta and Madeira.

In the 1970s, new district registration offices were opened, and letters reserved for them: EM and EV for Évora, ZA and ZB for Braga, ZC and ZD for Vila Real, ZE and ZF for Aveiro, ZG and ZH for Guarda, ZI and ZL for Santarém, ZM and ZN for Setúbal and ZO and ZP for Faro.

In the early 1980s the reservation of letter sequences by zone was discontinued, and vehicles were registered sequentially at a national level, so that letter combinations previously reserved for Oporto and Coimbra might be seen on vehicles registered in the Lisbon offices of the National Registration Office.

The type of plate also changed to black characters on a reflective white background, with the blue ribbon, with the emblem of the European Communities (now Union) on the left-hand side and the letter P as a country identifier.

However, in 1997 the combinations KA to KZ, the first letter of which sequence does not occur in the Portuguese alphabet and so had not previously been used, were given over to preregistered imported vehicles.

The authorities issue a registration number, and it is then the owner's responsibility to have a standardized plate made up, either of plastic or metal, on production of the appropriate documentation.

The Portuguese models of car plates were adopted - with the necessary local adaptations - by the then existing overseas territories of Portugal.

At the beginning, the model of 1911 was followed, with each licence plate number consisting of an initial letter or group of letters identifying the registration zone followed by a serial number (e.g. G–1234 for a car registered in Portuguese Guinea or CVS–1235 for one registered in the south-east zone of Cape Verde).