This arrangement keeps the machinery and accommodation away from the inflammable cargo. Modern tankers are efficient and flexible, capable of carrying crude oils or products such as fuel oil, naphtha, jet fuels or lubricating oils. Crude oils are often moved long distances in large tankers - the largest can carry 3 million barrels of oil. Products, on the other hand, are generally carried shorter distances on smaller tankers, about 30,000 dwt. These vessels have a large number of tanks and more complex pumping and piping arrangements to keep the cargo types separate.
Some carriers can carry both heavy and light crude oil and refined products.
Ten years ago, the average 250,000 dwt tanker consumed over 200 tons of fuel per day at full speed. Today's new tankers consume less than a third of that and fuel consumption can be cut even further by reducing speeds. Since fuel accounts for one-third of operating costs, such savings are important. Manning costs are also kept under close scrutiny, with crews averaging only 20 people, but without compromising high technical and safety standards. The most convenient way to move oil overland is to pump it through a pipeline.