OAKLAND, Calif. The Iranian vice president is threatening to use Iran's navy to close the Strait of Hormuz to shipping traffic if the U.S.-led oil embargo chokes off his nation's oil exports.Both outcomes are extremely unlikely. Moreover, the United States would not need to take military action even if Iran did resort to such an irrational act.The history of economic sanctions shows that they rarely work. Because economic transactions, unlike military actions, are mutually beneficial to the parties involved, countries usually advocate banning products they don't trade in, agree only rhetorically to sanction products they do purchase, and often attempt to evade the measures legally or illegally anyway.The tentative European oil embargo on Iran is a timely example. France and Germany, which import little oil from Iran, want to be tough, while Italy, Spain, and Greece, which are all in serious economic trouble and thirsty for cheap Iranian oil, have been exempted from the embargo for more than the six months that other European countries have been given to find new suppliers.Historically, embargoes erode over time as the target finds new ways to evade the sanctions and discounts its products to find alternative buyers. The Europeans have conveniently given themselves and Iran plenty of time to make that happen.Oil is a valuable commodity and Iran will find willing buyers sanctions or no sanctions. Thus, Iranian oil exports probably will not be cut off and Iranian officials won't have to act on their threat.Besides, closing the Strait would be economic suicide for the Iranian regime, which has been teetering politically since its fraudulent 2009 election. Such an action would indeed fulfill the West's goal of stanching Iran's oil exports, but it would also cut off vital imports, including refined petroleum products.Even during Iran's radical revolution in the late 1970s and its bitter war with Iraq from 1980 to 1988 which involved the belligerents attacking oil tankers and facilities and a large battle between the Iranian and U.S. navies Iran did not try to totally block this chokepoint. Thus, Iran's threat is likely just an attempt to increase the world oil price to nullify any effects of sanctions.In the unlikely event that Iran did try to close the Strait by using mines, suicide boats or anti-ship cruise missiles, it would be harder than commonly believed.Oil tankers are huge, have double hulls, and are difficult to sink, even with cruise missiles. During the Iran-Iraq war some tankers sustained five missile hits and survived. In addition, the range of these land-based missiles doesn't cover the entire Strait, which has several passages. Tankers also produce huge bow waves, which would make it difficult for small suicide boats to get near them.Mining the Strait would be difficult as well, requiring a large number of Iran's primitive mines to completely close the waterway. Capable regional air forces, such as Saudi Arabia's, could prevent that by sinking Iranian tankers and mine-layers without any need for direct U.S. involvement.U.S. Navy war games have shown that closing the Strait for any length of time would be highly unlikely. Even if oil flow through the Strait was reduced, more oil could be transferred from the Persian Gulf using the underutilized land pipeline across Saudi Arabia to its port of Yanbu on the Red Sea.History shows that developed economies, such as that of the United States, are fairly resilient to petroleum price increases that reduced oil flow might bring. Thus, there is no reason for the United States to use military force to keep the Strait open.Ivan Eland is author of No War for Oil: U.S. Dependency and the Middle East and a senior fellow with the Independent Institute, 100 Swan Way, Oakland, CA 94621; website: www.independent.org.