The Buenos Aires Great Southern Railway (BAGS) was one of the Big Four broad gauge, 5 ft 6 in, British-owned companies that built and operated railway networks in Argentina. The company was founded by Edward Lumb in 1862 and the first general manager was Edward Banfield after whom the Buenos Aires suburban station of Banfield was named, when it opened in 1873. After president Juan Perón nationalised the Argentine railway network in 1948 it became part of the state-owned company Ferrocarril General Roca.

The railway natinalisation in Argentina occurred on March 1, 1948, during President Juan Perón's first term of office, when the seven British- and three French-owned railway companies then operating in Argentina, were purchased by the state. These companies, together with those that were already state-owned, where grouped, according to their track gauge and locality, into a total of six state-owned companies which later became divisions of the state-owned holding company Ferrocarriles Argentinos.