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The biggest ships in the world are the supertankers that carry oil. The United States depends on these ships because the U.S. imports millions of barrels of oil every day. Most of it arrives on supertankers.

A typical supertanker holds about 2 million barrels of oil and is approximately 1,000 feet long. The biggest supertankers weigh more than a billion pounds once they are loaded up. The biggest supertanker ever built is named the Knock Nevis. It holds 4 million barrels of oil (about 170 million gallons) and is more than 1,500 feet long. After a long career on the open ocean, it is now a floating storage tank.

How do you get a ship this large moving? It takes a huge engine - the largest diesel engines in the world. A typical engine might produce 30,000 horsepower. The size of these engines is difficult to visualize, but imagine two or three city buses stacked on top of each other. An engine like this burns tens of thousands of gallons of diesel fuel per day.

Loading a ship this big takes time. A loading platform for a supertanker might have three flexible pipes to fill the ship. The pipes are 16 inches in diameter and each one pumps 75,000 barrels of oil per hour. Even with all that, it takes nine or 10 hours to load the ship.