Member states of Mercosur

Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is also the world's fifth-largest country by area and the seventh-largest by population, with over 213 million people. The country is a federation composed of 26 states and a Federal District, which hosts the capital, Brasília. Its most populous city is São Paulo, followed by Rio de Janeiro. Brazil has the most Portuguese speakers in the world and is the only country in the Americas where Portuguese is an official language.

Argentina, officially the Argentine Republic, is a country located in the southern cone of South America and with a claimed portion of Antarctica. It covers an area of , making it the second-largest country in South America after Brazil, the fourth-largest country in the Americas, and the eighth-largest country in the world. Argentina shares the bulk of the Southern Cone with Chile to the west, and is also bordered by Bolivia and Paraguay to the north, Brazil to the northeast, Uruguay and the South Atlantic Ocean to the east, and the Drake Passage to the south. Argentina is a federal state sub

Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the Atlantic Ocean to the southeast. It is part of the Southern Cone region of South America. Uruguay covers an area of approximately . It has a population of almost 3.5 million people, of whom nearly 2 million live in the metropolitan area of its capital and largest city, Montevideo.

Paraguay (), officially the Republic of Paraguay, is a landlocked country located in the central region of South America. It borders Bolivia to the northwest and north, Brazil to the northeast and east, and Argentina to the southeast, south, and west. Paraguay has access to the Atlantic Ocean via the Paraná–Paraguay Waterway. The country is governed as a unitary presidential republic composed of a capital district and seventeen departments. Its capital and largest city is Asunción.