The Engesa EE-T1 Osório was a Brazilian main battle tank prototype developed by Engesa. The tank was intended to be sold first to Arab and other Third World countries, jump-starting production — and enabling the Brazilian Army to later place its own orders without having to fund development costs. Development of the tank was initially privately funded by Engesa, but cashflow issues eventually led to the Brazilian government extending a loan to assist the program. Two prototypes of the tank were built, but the EE-T1 was never adopted for service.

Engesa was a Brazilian company in the oil and later automotive and military sectors founded in 1958. In the 70s and 80s it established itself as one of the "big three" in Brazil's arms industry, alongside Avibras and Embraer. It manufactured 6,818 land military vehicles such as the EE-25 truck and the EE-9 Cascavel and EE-11 Urutu armored vehicles, which it sold to Brazil and 18 other countries, and are still used in conflicts today. Its technological peak was the prototypes of the EE-T1 Osório main battle tank. Its founder, José Luiz Whitaker Ribeiro, was called the "civil armaments czar". In the civilian market, it became known with its Engesa 4 jeep. It went into decline at the end of the 80s as a result of mismanagement and a hostile internal and international environment, going bankrupt in 1993.