"EL PETROLEO es nuestro!" ("The oil is ours!"). This cry, which rang out in the streets when President Lázaro Cárdenas nationalised the oil industry in 1938, still resonates in Mexico. Bizarrely, it is used as a slogan both by the government, which is proposing to throw open the oil industry to private investment, and by those trying to organise a referendum against the move. Few countries in the world (not even Cuba or North Korea) have such a stranglehold over their oil; the state controls everything from the bottom of the well to the tip of the petrol pump. Yet in other respects Mexico is an open economy; foreigners even own its favourite beer, Corona. Why should oil be so sacred?

The answer is that oil is as much a historical asset for Mexicans as an economic one. For many countries independence from colonial rulers is their defining act of sovereignty. Mexico, too, celebrates the independence it won from Spain in 1810, but after that it lost half its territory to the United States in 1848, and continued to let foreign firms plunder its oil until even after the 1910-17 revolution. When Mr Cárdenas seized the oil industry overnight from the hands of British and American companies that had resisted unionisation in the 1930s, it was celebrated like a great victory against imperialism; people lined up to hand over everything from chickens to jewellery to help pay for the expropriation. Lorenzo Meyer, a left-wing Mexican historian, argues that reversing course 75 years later and allowing private and foreign investment would make 1938 just another in a long line of "historic defeats".

That is going too far. Mexico can tax and regulate its energy industry well enough, as countries like Colombia do, to get at least as much reward from its oil as it does now, while letting the private sector bear part of the risk. The problem is, Mexicans don’t trust their governors—or their regulators. They have watched the privatisation of Telmex, the telecommunications firm, make Carlos Slim the richest man in the world, at little benefit to themselves. Their foreign-owned banks are models of shoddy service. They fear that the biggest benefits of energy liberalisation will accrue to the few, not to Mexicans at large.

That is why the government needs to create a new narrative about its oil, rather than cynically claim that it remains faithful to the old one. Oil may nominally belong to all Mexicans, but the bureaucracy and the oil-workers' union currently benefit disproportionately from it. It is also a dwindling asset. If properly regulated, private investment can help diversify Mexico's supply of hydrocarbons, tapping deep-water oil and shale gas, for example, and cutting their costs. Cheaper energy would help Mexico become more competitive, as it has the United States. That would be a modern-day victory worth celebrating.