Over the last decade, Presidents in Argentina have formed large (oversized) legislative coalitions. From 1984 to 1995 legislative coalitions were made up an average of 105 deputies, yet from 1996 to 2007 this number had climbed to over 135 national deputies. What accounts for this variation? This paper argues that the denationalization of the political system complicates the coalition building process in the national legislature. To overcome the problems of exchange within and among parties that this process causes, the federal government has responded by building larger coalitions. This study presents a statistical model which estimates how the denationalization of the main political parties affects the size of the legislative coalitions.