A supertanker is one of the largest ships ever built, designed to carry massive quantities of crude oil across oceans. The term generally refers to Very Large Crude Carriers (VLCCs) and Ultra Large Crude Carriers (ULCCs), vessels capable of transporting roughly 2 million barrels of oil in a single voyage. These ships stretch longer than most skyscrapers are tall, and their sheer size creates unique challenges for ports, navigation, and environmental safety.
Size Classes and What They Mean
Supertankers are classified by deadweight tonnage (DWT), a measure of how much total weight a ship can carry, including cargo, fuel, crew, and supplies. VLCCs carry up to around 320,000 DWT, while ULCCs exceed that threshold. To put those numbers in practical terms, a single VLCC carries approximately 2 million barrels of crude oil, enough to supply a mid-sized country’s refinery for days.
Below the supertanker category sit smaller tanker classes like Suezmax and Aframax, each named for the waterways they can fit through. Aframax vessels can transit the expanded Panama Canal locks. Suezmax ships, as the name suggests, are sized for the Suez Canal. VLCCs and ULCCs are too large for the Panama Canal entirely, and only some VLCCs can squeeze through the expanded Suez Canal dimensions.
Physical Dimensions
A typical modern VLCC stretches 300 to 330 meters long (roughly 980 to 1,080 feet), with a beam (width) of about 55 meters and a draft of 28 meters when fully loaded. That draft, the distance from the waterline to the bottom of the hull, is what makes these ships so difficult to accommodate in most ports.
The largest supertanker ever built was the Seawise Giant, a ULCC completed in 1979 by Sumitomo Heavy Industries in Japan. After modifications, it measured 458.45 meters long (1,504 feet), making it the longest self-propelled ship in history. It was longer than the Petronas Towers are tall. Its deadweight tonnage reached 564,763 tonnes, a record that still stands. The Seawise Giant changed names several times over its life, including Jahre Viking and Knock Nevis, before being scrapped in India in 2009 and 2010. Breaking apart a ship that enormous took nearly a full year.
How Supertankers Load and Unload
The enormous draft of a fully loaded supertanker means most conventional ports simply aren’t deep enough. Shipping channels and harbors are regularly dredged to maintain depth for normal vessels, but a VLCC sitting 28 meters below the waterline needs exceptionally deep water. Countries that export large volumes of crude oil, like Saudi Arabia, often use offshore jetties that extend into naturally deep water where VLCCs can load directly.
In the United States, the situation is more constrained. All major Gulf Coast petroleum ports sit in inland harbors connected to the ocean through shipping channels or navigable rivers, and none of those waterways are deep enough for a fully loaded VLCC. The Louisiana Offshore Oil Port (LOOP), located offshore in the Gulf of Mexico, is currently the only U.S. facility that can handle a fully loaded VLCC. Plans have been proposed near Corpus Christi, Texas, to build additional deepwater export terminals capable of filling these massive ships completely. Until then, VLCCs calling at U.S. Gulf ports typically load partially, then top off at deeper facilities or transfer cargo from smaller ships at sea.
Why They Exist
Supertankers exist because of basic economics: the larger the ship, the cheaper it is to move each barrel of oil. Doubling a ship’s capacity doesn’t double the crew size, fuel consumption, or construction cost. This principle, called economies of scale, drove shipbuilders toward ever-larger vessels throughout the 1960s and 1970s, when global oil demand was surging and long-haul routes from the Middle East to Europe and Asia needed maximum efficiency.
VLCCs remain the workhorses of global crude oil transport today. They primarily operate on long routes between major oil-producing regions (the Persian Gulf, West Africa, the Americas) and refining centers in Asia, Europe, and North America. A single VLCC voyage can take weeks, and at any given time, hundreds of these ships are crossing the world’s oceans simultaneously.
Double Hulls and Safety Requirements
Supertankers today are built with double hulls, meaning the cargo tanks are surrounded by an inner and outer layer of steel with a gap between them. This design dramatically reduces the risk of oil spills if the outer hull is punctured in a collision or grounding. The International Maritime Organization (IMO) adopted the double hull requirement for new tankers in 1992, and then applied it retroactively to existing ships starting in 1995, giving older single-hull tankers a phase-out timeline based on their age.
That timeline was accelerated twice. After the tanker Erika broke apart off the coast of France in December 1999, spilling thousands of tonnes of heavy fuel oil, IMO member states pushed through stricter deadlines in 2001. Further revisions in 2003 accelerated the schedule again. By 2005, single-hull tankers were banned from carrying heavy grade oil, and all remaining single-hull ships were required to convert or retire by a set age, up to 30 years old. The result is that virtually every supertanker operating today has a double hull.
Life and Death of a Supertanker
A supertanker’s operational life typically spans 20 to 25 years of active service. Some ships transition to a second career as floating storage units, permanently moored in oil fields to hold crude oil before it’s transferred to smaller vessels. The Seawise Giant spent its final years doing exactly that, anchored in Qatar’s Al Shaheen Oil Field under the name Knock Nevis before its last voyage to the scrapyard.
When supertankers reach the end of their useful life, they’re typically beached at ship-breaking yards, most commonly in South Asia. Workers dismantle them piece by piece, recovering steel and other materials for recycling. For the largest ships, this process can take many months. The Seawise Giant, renamed Mont for its final journey, was beached in December 2009 at Alang, India, and scrapping continued through the end of 2010. During the Iran-Iraq War, this same ship had been attacked and damaged by Iraqi aircraft in 1988 while carrying Iranian crude oil, only to be repaired and returned to service in 1991 after being purchased for $39 million. Few machines on Earth have stories as eventful as the ships that carry the world’s oil.