This report analyses pension reform trajectories in Chile, Peru, and Colombia from a comparative political economy perspective. Using administrative coverage data and process tracing, it shows that structural reforms introduced in the 1980s and 1990s produced persistent ceilings on contributory coverage, largely due to labour informality and fragmented employment histories. These limits generated pressure for compensatory and hybrid reforms, including the expansion of non-contributory pillars and partial recalibration of contributory systems. While all three countries converged toward mixed pension architectures, their reform paths diverged according to political coalitions, institutional constraints, and degrees of instability. The findings highlight the structural limits of contributory expansion in high-informality contexts and underline the importance of reform sequencing and political feasibility for sustainable pension design.