Commented on by Jihad Watch here, the Iranians have invoked their standard threat to the West in the event of UN sanctions: Closing the Persian Gulf. Comments to the Jihad Watch post alone are worth the price of admission.
I suggest you visit the Energy Information Administration site for this page titled "Persian Gulf Oil and Gas Exports Fact Sheet." All part of the EIA "World Oil Transit Chokepoints" series.
The Iranians may be feeling their oats (and counting their chickens) after the apparently successful completion of a couple of mini-submarines (photo liberated from The Stupid Must be Punished).
Caption for top photo:
This oblique, north looking view shows the Strait of Hormuz (25.5N, 56.0E) which connects the Persian Gulf, to the left, with the Gulf of Oman, to the right. The mainland of Iran is at the top, north, and the Musandam peninsula lies to the south. ... the largest island is that of Kishm.To the right of Kishm island are the smaller islands of Hormuz, top, and Larak, below.(photo from NASA but retrieved from here, which is part of an interesting site all about Hormuz). Some interesting photos of some of the islands in the Strait here a site with information on sport diving in the Strait