[eCa]

Those are mostly oil tankers. Since 20% of the world's oil passes through the Strait of Hormuz [1], the Iranians threat of closing that passage has petroleum prices recently. More analysis at The Oil Drum [2].

[1] http://en.wikipedia.org/wiki/Strait_of_Hormuz

[2] http://www.theoildrum.com/node/8956