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Yet another way Iran could drive up oil prices is by threatening free passage of oil through the Straits of Hormuz or by engaging in naval mining in the Gulf (by its surface fleet of fast boats or with its smaller submarines) and other key locations (as it did in the late 1980s). Iran has already deployed anti-shipping missiles at Qeshm, Abu Musa Island, and on Sirri Island, all of which are in range of shipping through the Strait. It has also occupied and fortified three islands inside the shipping lanes of the Strait of Hormuz -- Abu Musa, the Greater Tunbs, and the Lesser Tunbs. Given that one-fifth of the world's oil flows through the Straits (as well as roughly a quarter of America's supply of oil) and that no other nation has fortified its shores near Hormuz, an Iranian threat to disrupt commerce there would have to be taken seriously by commercial concerns (e.g., insurers and commodity markets) and other nations.