Why doesn't petrol go down in Mexico? Along with the price of fuel we pay five taxes: three IEPS and two IVAs. La falsa idea del subsidio is a book that offers an overview of the process of contemporary modification of the rules established in the Law of the Special Tax on Production and Services that have endorsed three different IEPS taxes on fuel and two value-added taxes; it also makes an approximation of the calculation of the components of the price of fuel after the price liberalisation of 2017. The author asserts that the way in which the administrative authorities determine fuel prices and taxes is illegal and unconstitutional, as it violates the principle of double taxation, contrary to the principles of tax certainty, proportionality, legality and constitutionality. The study concludes with a proposal for a simple solution that would seem to be a quick corrective measure to the fiscal situation and problem that we suffer in the country, mainly in the border region, especially because of the price competition with the southern United States.