Big ships carry oil. 

Big ships carry oil across the sea. 

Long ago, people used wooden barrels. Barrels were heavy and could leak. They were also very expensive. 
Some tankers are very, very large. They are much bigger than most buildings.
An oil tanker is a large ship. It moves oil across the sea. 

Long ago, people used wooden barrels to move oil. Barrels were heavy and expensive. They also leaked often. Early ships used these barrels in their holds. This was not safe. The oil could slosh side to side. This could make a ship tip over. 
To fix this, designers built fixed tanks into the ship. They used walls called bulkheads to divide the space. This stopped the oil from sloshing too much. This helped the ship stay steady at sea.
Some tankers are very big. These are called supertankers. They move a lot of oil at once. This makes the cost of transport low.
An oil tanker is a special ship built to move oil across the sea. These ships are very important for moving energy around the world. There are two main types of tankers. Crude tankers carry unrefined oil from the place it is taken from the ground to a refinery. Product tankers are usually smaller. They carry refined products from refineries to places where people need them. 

In the past, moving oil was a very hard job. People used wooden barrels to carry oil on boats. This caused many problems. The barrels were very heavy and expensive. They also leaked and were often used only once. 

Modern tanker design began to take shape in the late 1800s. In 1876, the Nobel brothers started a large company in Baku, Azerbaijan. They worked with a builder named Sven Alexander Almqvist. He built the Zoroaster, which was the first successful oil tanker. The Zoroaster was 150 feet long and used two iron tanks. 
As time went on, tankers grew to be incredibly large. In the 1970s, shipowners built ultra-large crude carriers to move more oil for less money. The Seawise Giant was the largest supertanker ever built in 1979. It was 1,504 feet long and could hold 564,763 barrels of oil. 
You can think of an oil tanker like a giant floating warehouse. Just as a truck carries goods to a store, these ships carry the energy needed for many things. Some tankers even act as moving gas stations. These are called naval replenishment oilers, and they can fuel other ships while they are moving. 
An oil tanker, also called a petroleum tanker, is a massive ship designed for the bulk transport of oil. These vessels are essential to the global economy. They move the energy needed for many industries and daily lives. There are two primary types of tankers based on their specific jobs. Crude tankers carry unrefined crude oil from extraction sites to refineries. Product tankers are generally much smaller. They carry refined products from refineries to markets where people consume them. 
Tankers are classified by their size and their specific occupation. Sizes range from small inland or coastal tankers to massive ultra-large crude carriers (ULCCs). The scale of these ships is enormous. Tankers move a huge portion of the world's oil every year. Moving crude oil by tanker is very efficient. The average cost of transport is only US$1.50 per barrel. This makes them nearly as efficient as pipelines. 
Early methods of moving oil were very difficult and inefficient. In the 1850s, oil from Upper Burma was moved in earthenware vessels. Later, in the 1860s, Pennsylvania oil fields used wooden barrels. These barrels caused several major problems. They were very heavy, with the wood making up 20% of the total weight. Barrels were expensive and often leaked. In the early Russian oil industry, barrels accounted for half the cost of production. 
Designers eventually moved away from barrels to improve safety and stability. Early ships used makeshift wooden or iron tanks in the hold. This raised the center of gravity and increased fire risks. To fix this, engineers began incorporating fixed iron tanks into the hull. They used bulkheads, which are internal walls, to divide cargo into separate compartments. This prevented the free-surface effect. This effect occurs when liquid sloshes from side to side, which can cause a ship to capsize. 
Modern tanker technology evolved significantly in the late 19th century. In 1876, the Nobel brothers founded Branobel in Baku, Azerbaijan. They worked with builder Sven Alexander Almqvist to create the Zoroaster. The Zoroaster was the first successful oil tanker. It was 150 feet long and carried 1,000 tons of kerosene. It used two iron tanks separated by the engine room. 
Another major advancement came from British engineer Colonel Henry F. Swan. He designed the Glückauf, which was the first dedicated steam-driven ocean-going tanker. This ship allowed oil to be pumped directly into the hull. It featured cargo valves on the deck and a vapor line. Swan also used longitudinal bulkheads to divide tanks into port and starboard sections. This design virtually eliminated stability problems caused by sloshing oil. 
In the 1970s, the industry entered the supertanker era. Shipowners realized that larger tankers were more economical. After the 1956 Suez Crisis, ships had to travel around the Cape of Good Hope. This encouraged the building of much larger vessels. A typical WWII-era T2 tanker held 50,000 tons. In contrast, ULCCs built in the 1970s were much larger.
The largest supertanker ever built was the Seawise Giant. It was completed in 1979 at the Oppama shipyard. This ship was 1,504 feet long and held 564,763 barrels of oil. It was so large that it could not navigate the English Channel. Today, the largest working supertankers are the TI Europe and TI Oceania. These are the first ULCCs to feature a double hull for safety. 
Specialized tankers serve many unique roles in the maritime world. Naval replenishment oilers can fuel other moving vessels at sea. 
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