A rapidly growing body of research suggests that democracy enhances prospects for the peaceful settlement of interstate conflicts. To what extent can democracy also be linked with increased international cooperation? Building upon the literature on political cooperation as well as recent discussions of the “democratic peace,” this study offers a plausibility probe of the hypothesis that democracy increases the likelihood of interstate agreement. The analysis, which draws upon a data set covering dyadic interactions among Mercosur nations during the 1947–1985 period, utilizes both logistic regression and negative binomial regression methods to assess the relationship between democracy and cooperation. The findings offer only limited support for the hypothesis that democracy promotes cooperation and challenge the recent literature on the relative peace among democracies in several theoretically suggestive ways. The study points to the potential fruitfulness of more extensive and rigorous research on the nexus between domestic institutions and international cooperation.