Abstract
Public-private partnerships (PPP) as suppliers for public services have been increasingly used as an instrument for improving public policy, mostly when it comes to reducing costs and improving public transport. The purpose of this paper is to carry out a comparative analysis between two metropolitan areas in Mexico and to identify the main causes that explain the performance and difficulties of a hybrid supplying model. The transport sector was chosen not only for its great importance in urban areas but also due to its representativeness to highlight the specificities of PPPs. The Mexican experience has shown that infrastructure projects tend to underestimate their costs and to overestimate their demand, even with supposed formal validation processes. In this sense, even though PPPs have been generally promoted by international organizations, there is a prevailing need to explore the implications and challenges that emerge from this kind of governance tools. Process tracing was conducted as a methodological technique within a comparative approach using qualitative information.