This thesis deals with the issue of different efficiency between two integrational organizations in Latin America: Andean Community, and Union of South American Nations, by using neoliberal theory of international relations to examine he causes as to why the Andean Community is more efficient than the Union of South American Nations. First, the theoretical definition of neoliberal theory and the concept of cooperation problems are discussed. Then, follow chapters describing integration in Latin America, in general with all its characteristics, and a chapter describing history and basic institutional settings of the two organizations. In the practical part, each cooperation problem is either applied to the organizations and a relation between these problems and institutional setting, number of member states, and homogeneity between member states is examined. In the conclusion, the all three cooperational problems are brought together to determine, whether the main cause of different efficiency is the institutional setting and number of member states, or the homogeneity between members.