Argentina and Brazil have agreed to build a joint nuclear reactor to address looming energy shortages.
Energy dominated the first of two days of talks between the leaders
The agreement came as part of a plan by South America's two biggest economies to extend defence and energy projects.
It was announced after talks in Buenos Aires between Argentine President Cristina Fernandez and her Brazilian counterpart, Luiz Inacio Lula da Silva.
Brazil would export electricity to Argentina in the winter months ahead amid shortage fears, Mr Lula said.
"We're going to launch a satellite jointly and develop a nuclear project," said Mr Lula.
He added that the venture would "serve as an example in this world, ablaze with the temptation to build up arms and with political and ideological intolerance".
Each country currently has two operating nuclear plants, and both have signed the Nuclear Non-Proliferation Treaty.
Bolivian gas dispute
The two leaders see the joint nuclear project as a way to increase energy supply while raising their profile on the international stage, says the BBC's Americas editor Warren Bull.
But while energy issues dominated the first of two days of talks, the two presidents did not refer directly to a dispute over the ratio of Bolivian gas supplied to the two countries.
La Paz currently prioritizes its exports to Brazil, its biggest client, which imports 30 million cubic metres of Bolivian natural gas per day.
Argentina imports a maximum of 7.7 million cubic metres per day from Bolivia, and would like a bigger share.
There are fears it could suffer from acute energy shortages during the southern hemisphere's winter months ahead.
It is hoped the issue will be resolved during a joint meeting with Bolivian President Evo Morales on Saturday.