By Elliott Gotkine
BBC correspondent in Buenos Aires
The South American trade bloc, Mercosur, has accepted Mexico and Venezuela as associate members.
Oil-rich Venezuela is set for an energy alliance with Argentina
The announcement came on the final day of Mercosur's presidential summit, which was held this year at the Argentine resort of Puerto Iguazu.
Trade agreements were also reached with India, South Africa and Egypt.
Argentina will now transfer the rotating six-month presidency to Brazil.
The 26th Mercosur Presidential Summit got off to the worst possible start when just hours before it was due to begin, Argentina decided to impose restrictions on certain Brazilian imports, in a bid to protect its domestic industry.
But by the time the two-day gathering ended, significant progress had been made on several issues, and the row between Buenos Aires and Brasilia appeared to have subsided.
Among the most important agreements was the decision to accept Mexico and Venezuela as associate members of Mercosur, a status already enjoyed by Chile, Bolivia and Peru.
Mercosur went on to invite Mexico to continue free trade talks, with a view towards its eventual full admission to the South American trade bloc.
Elsewhere, Venezuela's President, Hugo Chavez, occupied much of the media's attention.
Just weeks before facing a recall referendum that could put an end to his presidency, he agreed to form a strategic energy alliance with Argentina, called Petrosur.
Mr Chavez hopes other state-owned energy companies, like Brazil's Petrobras, will join in the future.
The Venezuelan leader, who has clashed with privately-owned TV channels in his home country, also signed an agreement with Argentina to create a bilateral state television channel, which he hopes will one day compete with international news organisations.