Have Somali pirates landed their best bounty yet? They have hijacked an oil tanker headed to the United States, posing a huge environmental and security threat to the region. The Greek-owned Maran Centaurus has the capacity to hold 300,000 tons of crude oil, though the size of its cargo is unclear. Still, it is likely to be worth millions of dollars. "You're sitting on a huge ship filled with flammable liquid. You don't want somebody with a gun on top of that," said a piracy expert.