Line G is a planned addition to the Buenos Aires Underground which has been on the drawing board in numerous forms since the 1930s.

After a failed attempt at financing and building the line in 2009, its most recent proposal was put forward in 2015 by the government of Buenos Aires.

[2][3] The Retiro - Cid Campeador line, which was to stretch 7.3km and have 11 station, was then planned as follows: By December 2009, the City of Buenos Aires had made significant advances in negotiating financing and construction equipment from Exim Bank of China and China Railway Group Limited (CREC).

[4] By early 2011, it was announced that the government had obtained financing for $1.4 billion for the line and was to begin construction in 2012, concluding in 2016.

[5] The line was to be 12.5km long and terminate further west at Villa del Parque, continuing on from the Sid Campeador terminus envisioned in Law 670.