Public (bus) transport in Tunisia has been a government affair and only recently limited involvement of private operators started. (for a history see TRANSTU page). Currently there are government companies in Tunis (TRANSTU), Sousse (STS) and in eleven provincies (Société Régionale de Transport du Gouvernorat de ..... (in Tunisia provinces are called "Gouvernorats")). Not all "gouvernorats" have their own bus company, some areas with low population density or that are too small are covered by routes from other regions. At national level there is a long distance company called SNTRI (Société Nationale de Transport Inter-urbain). Private companies include STCI (Société du Transport Confortable Interurbain) for long-distance routes, TUS and TUT on some (sub)urban services in Tunis. Finally we added Tunisair with airport and shuttle buses. Each company has its own page. Some company webpages also have interesting historical information.
Government owned buses have red-on-white registration plates starting with 15 followed by a 5-digit number starting with 3. Private buses have white-on-black registration plates with a 2-digit number followed by the word "Tunisia" in Arabic script and another number of up to 4 digits. The government plates appear to have been introduced beginning of the 1990's as older pictures show buses with "normal" plates.
Buses are centraly bought and distributed over the various government companies. Fleets are therefore largely similar. Tunis, Sfax and Sousse have the largest fleets each, other companies are smaller. After some two decades during which only locally built buses were bought teh political and economic crises led to the import of 98 ex Paris buses to Sfax (SORETRAS) beginning of 2014.