An oil tanker, a common name for a liquid cargo carrier carrying oil or refined oil in bulk, is a type of vessel.

In a broad sense, it refers to a ship that transports various kinds of oil in bulk, including petroleum, petroleum products, various animal and vegetable oils, liquid natural gas, and LPG. Most of the oil tankers usually referred to are vessels transporting crude oil, while ships carrying finished oil products are called product tankers. Ships carrying natural gas and LPG in liquid form are referred to as liquefied gas ships.

In addition to tanks and pipes, tankers are equipped with boilers, propellers, generators, pumps (loading and unloading pumps on large tankers can pump tens of thousands of tons of liquid per hour), and fire-fighting devices.

Today's tankers carrying flammable liquids use a method of filling empty tanks with inert gas to prevent the risk of combustion or explosion. These inert gases displace the oxygenated air, leaving the empty tank inside the tanker almost completely devoid of oxygen.

Some ships use exhaust gases from the ship's power plant to refine the inert gas, while others fill the inert gas from the dock during unloading. The pumps used for unloading tankers are placed directly on board.

Today's tankers are equipped with cargo computers, as are most other ocean liners, which monitor the loading and unloading of cargo and calculate all the forces applied to the ship during the loading and unloading process.

Tankers are easily distinguished from other ships by their very flat decks, with little other than the cockpit towering above.

They do not require a deck crane to load or unload their cargo, but only a small crane in the middle of the tanker, which is used to lift the pipeline on the dock to the tanker and connect the pipeline system on the tanker. This pipeline system can be seen from a distance.

However, these large ships have their drawbacks; despite their walls being three to four meters thick, they still experience structural difficulties, and the forces exerted on them are so great that they can deform or crack.

Because of their deep draught, they can only call at a few ports. They cannot pass through the Panama Canal, although even a 450,000-ton tanker can pass through the Suez Canal when empty.

Most of the tankers carrying crude oil could carry up to 100,000 tons of cargo, and 90% used steam engines as power plants, because crude oil had to be heated before it was fluid enough to be pumped into the tankers, and they were kept heated throughout the transport so that they could be unloaded quickly at their destination.

The speed at which the crude oil is transported is not important, so the speed of these ships is generally around 15 knots (28 km/h), They are relatively slow ships.