Here's a neat map looking at how oil travels by sea around the globe — focusing on the key "choke points" where that oil supply is most vulnerable to attack:

Source: U.S. Energy Information Administration

That map comes from this recent reporting project on U.S. energy security by nine student journalists at the Medill National Security Journalism Initiative. The Web site is really worth a look — the reporters explored all aspects of energy security, from presidential rhetoric on the subject to the oil markets themselves to a breakdown of U.S. military operations to stabilize the oil supply. And the site has plenty of charts and graphs.

To accompany the map above, Dana Ballout has a piece looking in more detail at all the potential oil choke points — particularly the Strait of Hormuz, where 17 million barrels of oil pass through each day, or one-fifth of the world's supply. That includes this eye-opening figure:

Protecting oil tankers passing through the Strait of Hormuz, the narrow passage off the coast of Iran and the United Arab Emirates, is one of the critical missions of the Navy here. It is also expensive. By some estimates, the United States has spent as much as $8 trillion on maintaining such a menacing military presence in the region in recent decades, including aircraft carrier groups bristling with jet fighters, to make sure countries like Iran don’t choke off the world’s oil supply.

Roger Stern, a professor at the University of Tulsa National Energy Policy Institute, came up with the $8 trillion calculation in a 2010 study published in the Energy Policy Journal. He concluded that the U.S. has spent that sum on protecting oil resources in Persian Gulf since 1976, when it first began increasing its military presence in the region following the first Arab oil embargo.

Estimates of the actual cost vary. According to a 2009 study by the RAND Corporation, there is no official public U.S. accounting of the costs of protecting U.S. oil interests in the Persian Gulf or elsewhere. However, others like Stern have come up with numbers ranging from $13 billion to $143 billion per year.

Check out the whole reporting project here.