Five years ago, when Mexico transformed its energy sector, most commentators were worried about the government’s capacity to implement the reform. What would the upstream contracts look like? Would the auctions be transparent? How would international companies react? After two successful auction rounds, 107 signed contracts, and the creation of viable regulatory agencies to manage and monitor the reform agenda, the questions have changed. Today, Mexico’s capacity to implement energy reforms and attract foreign investment is no longer in doubt. Today, the most pressing questions about the reform concern its long-term sustainability. Can it survive the Mexican electoral cycles? Will Mexico continue down the same road that fosters private participation in the development of new fields? How safe are the current investments in Mexico from the rise of populism and nationalism in the Mexican political narrative? In other words, moving forward, are the necessary legal pillars cemented in place firmly enough to survive any political hurricane? The legal response to these questions, as with many legal issues, is unclear. This paper focuses on why the legal architecture of the energy reform for upstream activities is not as “bulletproof” and “irreversible” as some Mexican officials claim.