Mercosur is a full customs union encompassing Argentina, Brasil, Paraguay y Uruguay. Additionally, Venezuela, Ecuador, Chile, Bolivia, Colombia and Perú are associate members of the union, and as such, participate in the economic union, but not the unified customs system.

While Venezuela signed into the union in 2006, their membership has been blocked ever since by the parliament of Paraguay.

Venezuela has proven to be economically unstable and volatile under the leadership of leftist Hugo Chavez; however, given Paraguay’s persistent obstruction of the country’s membership, the leaders of Uruguay, Argentina , and Brazil have proposed rule changes to circumvent Paraguay’s legislature representing the citizens of Paraguay.

Since beginning in 1991, the economic and political agreement the block would now rank 4th in world population if it were a country, and 5th in GDP.

Ecuador is currently considering an invitation to Mercosur.

Recently, a similar economic agreement made up of largely western countries (Mexico, Chile, Peru and Colombia) named the “Alianza del Pacífico” has provided a regional counterweight to the 17 year old Mercosur. Alianza del Pacífico represents roughly 75% of the total population encompassed by Mercosur.