Venezuela became a full member of Mercosur at a summit of the South American regional trading bloc Friday while Bolivia took a first step toward joining.
Host country Brazil hailed Venezuela's entry, which marked the group's first enlargement since Argentina, Brazil, Paraguay and Uruguay founded it in 1991.
But Venezuelan President Hugo Chavez did not attend. The firebrand leftist leader appeared in public for the first time in three weeks on Friday as he returned home from Cuba after his latest cancer-related medical treatment.
Brazilian President Dilma Rousseff hailed the decision by Bolivia, a Mercosur associate member along with Ecuador, to take the first step toward full membership.
Ecuadoran President Rafael Correa said his country would decide early next year on whether to seek full membership amid concern about the impact integration might have on its dollar-based economy.
With the admission of Venezuela, which boasts the world's largest proven oil reserves, the bloc is now an energy and agricultural giant with a GDP of $3.3 trillion (83 percent of that of South America) and a population of 275 million.
Bolivia and Ecuador would boost Mercosur's population to nearly 300 million.
Uruguayan President Jose Mujica meanwhile said the summit would mull whether to jumpstart stalled negotiations on a free trade agreement with the European Union.
Negotiations have stumbled over differences on agriculture -- notably Europe's subsidies to its farmers, which undermine South America's efforts to sell its own products.
Argentine President Cristina Kirchner, whose country is embroiled in a World Trade Organization dispute with the EU and the United States, urged Mercosur to negotiate with Europe "as an equal".
She accused the Europeans of hypocrisy for alleging Argentine protectionism while they themselves, she said, have been practicing it for decades.
The Brasilia summit marks the end of Brazil's Mercosur presidency, which will pass to Uruguay for the next sixth months.