The Strait of Hormuz has never been closed. The threat of closure has been used repeatedly as a diplomatic instrument by Iran, and incidents in the strait have periodically elevated insurance premiums, rerouted tankers, and spiked oil prices. What has not happened, in the modern era of global oil dependence, is a complete cessation of transit. This absence of precedent does not mean the scenario is implausible. It means that the consequences of closure must be modeled rather than observed, and the models are sobering.