Why Iran can’t cut off your oil.
BY EUGENE GHOLZ | SEPT. / OCT. 2009

Supertankers carry about 90 percent of Persian Gulf oil exports
through the Strait of Hormuz each day, satisfying some 20 percent of
worldwide demand. For maximum safety, the International Maritime
Organization suggests that the huge, difficult-to-maneuver ships
travel within a designated channel while in the strait, but that
channel is only a few miles wide. With such a narrow passage, many
experts fear that an attacker (read: the Iranian military) could
“close the strait.”

The Iranians appreciate the concern: Explicit threats to the strait
are a key component of their foreign policy. Alternate routes could
only carry a fraction of the oil, so a disruption could cause a major
price spike that would severely threaten the global economy.

But the conventional wisdom may be wrong. Regardless of how we assess
the credibility of Iran’s threats, we should also assess Iran’s
capabilities. Iranian military exercises apparently emphasize three
weapons in the strait: small suicide boats, mobile antiship cruise
missiles, and sophisticated sea mines. Using these tools, how hard
would it be for Iran to disrupt the flow of oil?

The answer turns out to be: very hard. Iran would have to disable many
of the 20 tankers that traverse the strait each day — and then
sustain the effort. Iran cannot rely on the psychological effects of a
few hits. Historically, after a short panic, commercial shippers adapt
rather than give up lucrative trips, even against much more effective
blockades than Iran could muster today. Shippers didn’t stop trying
during World War I. Nor did the oil trade in the Gulf seize up during
the 1980s Tanker War, when both Iraq and Iran targeted oil exports.

Instead, tankers tend to move around dangers. The strait is deep
enough that even laden supertankers can pass safely through a 20-mile
width of good water, not just the 4-mile-wide official channel.
Tankers already take other routes when it is convenient; during a
conflict, they would surely scatter, as they did in the 1980s.
Although the strait is narrow compared with the open ocean, it is
still broad enough to complicate Iran’s effort to identify targets for
suicide and missile attacks. The area is too large to cover with a
field of modern mines dense enough to disable a substantial number of
tankers, especially given Iran’s limited stockpile.

What’s more, tankers are hard to damage with mines or the small
warheads on modern missiles. And a big ship pushes a tremendous amount
of water out of its way when it is moving; tankers’ bow waves would
fend off most small boats attempting suicide attacks. Terrorists hit
the USS Cole and the Limburg because their targets were stopped.

Surprisingly, oil tankers also do not burn well. They generally have
too much fuel and not enough oxygen to sustain a blaze. Only a tiny
fraction of their bulk contains sensitive equipment that, if damaged,
would disable the ship. The suicide attack on the Limburg was a lucky
shot that hit a boundary between a full cargo cell and an empty one
full of air, so the fuel-air mixture caught fire. Even so, three days
later, the ship was able to move under its own power, and after
repairs, it returned to the global tanker fleet. Over five years of
the Iran-Iraq War, 150 large oil tankers were hit with antiship cruise
missiles, but only about a quarter were disabled.

So what? By presuming that Iran can easily close the strait, Western
diplomats concede leverage, and the current U.S. habit of reacting
immediately and aggressively to Iranian provocations risks unnecessary
escalation. Iran would find it so difficult, if not impossible, to
close the strait that the world can afford to relax from its current
hair-trigger alert.