Development started in 1982 and the first prototype was completed in 1985.[1]

The EE-T1 was considered for service with the Saudi Arabian Army. It was evaluated against the French AMX 40, the American M1 Abrams, and the British Challenger 1 and emerged as the winner. The Osorio was quite cheap and affordable while having better results in the trials than the other three MBTs. In September 1989, Saudi Arabia quietly opted for the M1 Abrams instead and only announced its new decision shortly after Iraq invaded neighboring Kuwait, triggering the Persian Gulf War.[2] The two only prototypes were given to the Brazilian Army as a result of Engesa going bankrupt.