Tankers account for 36.9% of the global fleet by deadweight tonnage, making them the single largest category of commercial shipping by carrying capacity. Over 4000 tanker ships transport 2 billion metric tons of liquid cargo across the world’s ports. 

There are different types of tanker vessels purpose-built for the cargo type they move. For instance, crude oil tankers, which usually ply from the Gulf region to Asia; LNG carriers, which ship natural gas at -162 °C; chemical tankers, which carry industrial chemicals in stainless steel tanks; and even wine and vegetable oil, which are transported in food-grade vessels.

This article covers every classification system used in the tanker industry: cargo type, AFRA size, hull design, and trade route, with the specific figures that matter to anyone working in or studying the maritime sector.

What Is a Tanker Ship?

A tanker ship is a purpose-built vessel which carries liquid cargo in bulk, within sealed, pressurised, or temperature-controlled tanks integrated into the ship’s structure. 

Unlike bulk carriers, which carry dry goods in open holds, or container ships, which move packaged freight, tankers are designed keeping in mind the properties of the cargo they carry, its temperature, pressure, chemical reactivity, viscosity, and environmental hazard level.

The cargo tank arrangement runs along most of the vessel’s length, divided into port, starboard, and centre tanks separated by longitudinal and transverse bulkheads. This division serves two purposes: it limits the free surface effect of liquid sloshing under ship motion, and it reduces the risk of total cargo loss if the hull gets damaged.

Tanker crews use dedicated cargo pumps, pipelines, and manifold systems to load and discharge. Larger vessels can take 24 to 36 hours to complete a full discharge, with pumping rates on VLCCs reaching 10,000 cubic metres per hour.

Classification of Tanker Ships By Cargo Type

The most fundamental classification divides tankers by what they carry. This distinction drives every design decision: tank coating, temperature control systems, pumping arrangements, safety classification, and regulatory regime.

Crude Oil Tankers

Crude oil tankers transport unrefined petroleum from extraction points such as offshore platforms, onshore terminals, and pipeline endpoints to refineries. 

They are among the largest tankers afloat because crude moves in high volumes on fixed intercontinental routes.

Cargo tanks on crude carriers are bare steel, since crude oil is not corrosive to the tank structure and refined coatings are unnecessary. An inert gas system, mandatory under SOLAS, fills the vapour space above the cargo with exhaust gas or nitrogen to prevent explosive atmosphere formation during loading and discharge.

Primary trade routes for crude tankers include the Middle East Gulf to East Asia (the world’s busiest crude corridor), West Africa to Europe and North America, and the Caribbean to the United States Gulf Coast.

Product Tankers

Product tankers carry refined petroleum products from refineries to distribution terminals and storage facilities. 

Common cargoes include gasoline, diesel, jet fuel, kerosene, naphtha, and fuel oil. Unlike crude tankers, product carriers must prevent cross-contamination between cargoes of different grades.

Tank coatings, typically epoxy or zinc-based, protect the cargo from contamination by rust and protect the steel from corrosive products. 

Product tankers operate on more flexible routes than crude carriers, responding to regional price differentials and seasonal demand rather than fixed refinery supply chains.

The smaller size of most product tankers (General Purpose to Long Range 2 class) allows them to access a wider range of ports and terminals than the deep-draught crude carriers.

Chemical Tankers

Chemical tankers carry industrial chemicals, from commodity products such as methanol and caustic soda to highly hazardous substances such as vinyl chloride and sulphuric acid. 

The IMO’s International Bulk Chemical (IBC) Code classifies chemical tankers into 3 types based on the hazard level of the cargo they are approved to carry.

IMO Type 1 vessels are designed for the most hazardous chemicals; those posing very severe environmental and safety risks. In these ships, cargo tanks must be located at the maximum prescribed distance inboard from the ship’s shell plating, and the vessel must survive the most severe standard of structural damage. Cargoes such as certain alkaryl phosphate mixtures fall into this category.

IMO Type 2 vessels carry chemicals with appreciably severe hazards, requiring significant containment measures. Acetonitrile, despite being a lower-hazard Category Z substance under the IBC Code, requires Type 2 carriage due to its specific risk profile.

IMO Type 3 vessels handle chemicals with sufficiently severe but moderate hazards, such as n-alkanes, methanol, and palm oil. A moderate degree of containment is required, with less stringent tank positioning rules than Types 1 and 2.

Chemical tankers are typically fitted with multiple independent cargo tanks, often 20 to 40, allowing simultaneous carriage of different products without contamination risk. Tanks are constructed from stainless steel or coated with specialist linings depending on the cargo. Many chemical tankers also carry clean petroleum products and food-grade vegetable oils, making them highly flexible commercial assets.

Gas Carriers or LNG and LPG Ships

Gas carriers transport hydrocarbon gases that have been converted to liquid form, either by cooling, pressurisation, or a combination of both. The two primary categories, LNG and LPG carriers, have different engineering requirements.

LNG carriers transport liquefied natural gas at −162°C, the temperature at which methane becomes liquid at atmospheric pressure. 

Three cargo containment systems are in commercial use. 

Membrane systems (GTT Mark III and No. 96) use thin corrugated steel membranes supported by insulation and the ship’s inner hull; they are the most common design in large LNG carriers. 

Moss Rosenberg spherical tanks are self-supporting, independent spheres mounted above deck level; they are visually distinctive and structurally independent from the hull. Type B independent prismatic tanks occupy the space between the hull structures.

The largest LNG carriers, the Q-Max class operated by Qatar, have a cargo capacity of 266,000 cubic metres, roughly equivalent to 3.4 billion cubic feet of natural gas in vapour form. Standard LNG carriers typically range from 125,000 to 180,000 m3.

LPG carriers transport liquefied petroleum gas, primarily propane and butane, as well as ammonia and petrochemical gases. 

Three carriage methods exist, depending on the cargo and vessel size. Fully pressurised carriers store LPG at ambient temperature in cylindrical pressure vessels at up to 18 bar; they are typically small vessels under 5,000 cubic metres used for regional distribution. 

Semi-refrigerated carriers combine moderate pressure with cooling to around −10°C, serving mid-range trade routes. Fully refrigerated carriers maintain cargo at −48°C at near-atmospheric pressure and are the largest LPG carriers, with capacities up to 84,000 cubic metres.

Specialty and Commodity Tankers

Beyond hydrocarbons and chemicals, a category of tankers carries food-grade and specialty liquid commodities.

Vegetable oil and edible oil tankers carry palm oil, soybean oil, sunflower oil, and related products in tanks constructed from stainless steel or coated to food-grade standards. Cargo heating coils maintain viscosity during cold-weather transits.

Bitumen tankers carry bitumen (asphalt) at approximately 150°C to maintain it in pumpable liquid form. These vessels operate primarily between refinery bitumen terminals and road construction supply ports.

Wine tankers carry bulk wine in stainless steel tanks on European coastal routes, primarily between Spain, Portugal, and northern European bottling facilities. Typical cargo volumes range from 2,000 to 7,000 tonnes per voyage.

Fresh water tankers supply drinking water to islands, offshore platforms, and remote coastal communities without local sources.

Molasses tankers carry the viscous byproduct of sugar refining, requiring heated tanks and specialist pumping systems.

Classification of Tanker Ships by Size Using The AFRA Scale

The Average Freight Rate Assessment (AFRA) scale was developed in 1954 by Shell Oil to standardise tanker chartering contracts.

It classifies tankers by deadweight tonnage (DWT), i.e., the total weight of cargo, fuel, stores, and ballast a vessel can carry. The scale has become the global standard for tanker classification by size.

General Purpose and Medium Range Tankers

General-purpose tankers (10,000–24,999 DWT) and medium-range tankers (25,000–44,999 DWT) are the workhorses of refined product distribution. Their modest size allows access to the widest range of ports, including inland waterway terminals and small island harbours. MR tankers, the most numerous class in the global product tanker fleet, carry between 190,000 and 345,000 barrels of gasoline in a single voyage.

Long Range Tankers (LR1 and LR2)

Long Range 1 tankers, having a DWT ranging from 45,000 to 79,999 DWT, bridge the gap between product and crude trades. They can carry both clean petroleum products and dirty crude cargoes. 

Long Range 2 tankers (80,000–159,999 DWT) are sometimes called Panamax tankers, reflecting their maximum size for transit through the original Panama Canal locks. The expanded Neopanamax locks, opened in 2016, now accommodate vessels up to approximately 120,000 DWT.

Aframax

Aframax tankers, spanning 80,000 to 120,000 DWT, are dominant in regional crude oil trades. With a length of around 245 metres, a beam of 34 metres, and a draft of 20 metres, Aframax vessels can access nearly all harbour facilities worldwide, a commercial advantage that keeps them competitive against larger classes on shorter routes.

Aframax tankers operate extensively in the Mediterranean, Black Sea, North Sea, Caribbean, and East and South China Seas. Their flexibility makes them the preferred choice when a full VLCC cargo cannot be sourced or when port restrictions rule out larger vessels.

Suezmax

Suezmax tankers carry between 120,000 and 200,000 DWT and are originally defined as the maximum vessel size capable of transiting the Suez Canal in a laden condition. At approximately 285 metres in length, 45 metres beam, and 23 metres draft, a laden Suezmax can carry up to 1 million barrels of crude oil.

The Suez Canal’s expansion over successive dredging programmes has raised its maximum draft to 20.1 metres, allowing some Suezmax vessels to transit at partial load even above the original design limit. Suezmax tankers are the primary vessel class on the West Africa to Europe crude route.

Very Large Crude Carrier (VLCC)

VLCCs range from 200,000 to 319,999 DWT and represent the principal vessel class for long-haul intercontinental crude oil transport. They are usually 330 m long and carry 2 million barrels of crude oil per voyage.

Daily operating costs for a VLCC run approximately $10,000 to $12,000, excluding fuel. Charter rates fluctuate dramatically with market conditions, touching $309,601 per day at the 2007 market peak and collapsing to $7,085 per day in 2012 during the oversupply period. The largest single crude trade lane, the Middle East Gulf to East Asia, is almost exclusively served by VLCCs.

Did you know: A single VLCC cargo of 2 million barrels is approximately eight times the volume of oil spilt in the 1989 Exxon Valdez disaster.

 Ultra Large Crude Carrier (ULCC)

ULCCs exceed 320,000 DWT, with the largest vessels ever built reaching 564,000 DWT. They are 415 m long, 63 m wide and have a draft of 35 m. 

Due to their massive size, they cannot enter any conventional port when fully laden. Loading and discharge must take place at offshore single-point mooring terminals or purpose-built deepwater facilities.

The Knock Nevis (originally named Seawise Giant), at 564,763 DWT and 458.45 metres in length, remains the longest ship ever built; however, it was scrapped in 2010.

A fully laden vessel of that class required approximately 8 kilometres and 15 minutes to come to a complete stop.

The TI-class tankers, including the TI Europe, TI Asia, TI Africa, and TI Oceania, at 441,500 DWT each, are notable as the first double-hulled ULCCs, demonstrating that maximum size and modern safety standards are not mutually exclusive.

Classification of Tanker Vessels by Hull Design

Choosing the right Hull design is crucial in tanker construction since it determines the ship’s environmental risk profile and, as per the  MARPOL Annex I amendments, its legal eligibility to trade.

Single-Hull Tankers

These tankers feature a single steel layer between the cargo and the sea and dominated the market through the 1980s.

However, if there was a hull breach due to grounding, collision or structural failure, the cargo would be in contact with the environment.

The 1989 Exxon Valdez grounding in Prince William Sound, Alaska, which released approximately 37,000 tonnes of crude oil, triggered international regulatory action against this flawed design.

As a result, the MARPOL Annex I amendments, which were adopted in 1992, phased out single-hull tankers from international trade.

By 2010, single-hull vessels above 5,000 DWT were banned from carrying heavy grades of oil, and no new tankers of this type were built from 1990 onwards.

Double-Hull Tankers

As the name suggests, these tankers have a second inner hull separated from the outer shell by a void space, typically used as ballast tanks.

In case of hull damage,  the outer hull may be breached while the inner hull and cargo tanks remain intact, preventing or significantly limiting spillage.

Of the approximately 9000 tankers in the global fleet, almost all feature a double-hull construction.

The TI-class ULCCs, commissioned in 2002–2003, demonstrated that double-hull construction was viable even at the end of the size scale.

Classification of Tanker Ships by Trade Route

Trade route classification overlaps with size classification but reflects operational reality: where a tanker trades is as defining as what it carries.

Coastal tankers (under 50,000 DWT) operate within a single country’s territorial waters or between adjacent ports in the same region. They handle the last mile of liquid distribution, from storage terminals to industrial users, power stations, and bunkering facilities. Draft restrictions at small ports typically limit coastal tankers to 10 metres or less.

Short-sea tankers operate on intra-regional routes within the Mediterranean, the Baltic, Southeast Asian archipelagos, or the Caribbean with distances ranging from 500 to 3,000 nautical miles. This segment is dominated by MR and LR1 class vessels.

Deep-sea tankers conduct intercontinental voyages exceeding 5000 nm, from the Middle East to Asia, from West Africa to Europe, the United States Gulf Coast to Europe and Asia. VLCCs and Suezmax tankers dominate this segment, with voyage times of 20 to 45 days from loading to discharge.

The Largest Tankers Ever Built

The post-World War II oil boom drove rapid escalation in vessel size through the 1960s and 1970s, as shipping companies sought to exploit economies of scale on the Middle East–to–Europe and Middle East–to–Japan crude routes.

Seawise Giant (1979), later renamed Jahre Viking and then Knock Nevis, reached 564,763 DWT and 458.45 metres in length, making it the largest and longest ship ever built. 

Its draft of 24.6 metres meant it could not pass through the English Channel or the Suez Canal even in ballast. It was attacked and sunk during the Iran-Iraq War in 1988, salvaged, repaired, and returned to service before being scrapped in India in 2010.

TI Europe, TI Asia, TI Africa, and TI Oceania (2002–2003), at 441,500 DWT each, represent the largest double-hull tankers ever built. Constructed at Daewoo Shipbuilding in South Korea, they demonstrated the compatibility of MARPOL-compliant design with maximum cargo capacity. Two of the four vessels were converted to floating storage and offloading (FSO) units in the 2010s.

The reduction in average tanker size since the 1970s supertanker era reflects a structural shift in oil trade patterns, with more diverse supply sources, more varied destination markets, and infrastructure constraints,  rather than any engineering limitation on vessel size.

Frequently Asked Questions

1. What is the difference between a VLCC and a ULCC?

A VLCC (Very Large Crude Carrier) carries roughly 2 million barrels of crude oil, while a ULCC (Ultra Large Crude Carrier), which exceeds 320,000 DWT, has a carrying capacity of 3 million barrels. 

 VLCCs can access certain deep-water fixed terminals, while ULCCs require offshore single-point mooring systems at all loading and discharge points due to their extreme draft.

2. What is an Aframax tanker?

Aframax vessels are usually 245 m long and can access nearly all port facilities worldwide, making them the most commercially flexible class of crude carrier. They dominate regional crude trades in the Mediterranean, North Sea, and Caribbean.

3. What is a Suezmax tanker, and why is it named that?

A Suezmax tanker carries between 120,000 and 200,000 DWT, the maximum size originally capable of transiting the Suez Canal in a fully laden condition. 

At approximately 285 metres in length and 45 metres beam, a Suezmax carries up to 1 million barrels of crude oil. The Canal’s successive deepening has since allowed some larger vessels to transit in partial load.

4. What is the difference between a crude tanker and a product tanker?

A crude tanker carries unrefined petroleum directly from extraction points to refineries. A product tanker carries refined petroleum products like gasoline, diesel, jet fuel, and kerosene from refineries to distribution terminals. 

Crude tanker tanks are typically bare steel; product tanker tanks are coated to prevent cargo contamination and corrosion. Product tankers are generally smaller and operate on more flexible, market-responsive routes.

5. What are IMO Type 1, 2, and 3 chemical tankers?

The IMO’s IBC Code classifies chemical tankers by the hazard level of their approved cargoes. Type 1 vessels carry the most hazardous substances and must survive the most severe structural damage; their cargo tanks must be positioned at the maximum distance inboard from the ship’s side. 

Type 2 vessels carry appreciably hazardous chemicals with significant containment requirements. Type 3 vessels carry moderately hazardous substances with standard containment measures. Most chemical tankers are approved for Type 2 or Type 3 cargoes; purpose-built Type 1 vessels are rare.

6. What is the difference between an LNG carrier and an LPG carrier?

LNG (liquefied natural gas) carriers transport methane cooled to −162°C at near-atmospheric pressure; their tanks are cryogenic, highly insulated, and among the most technically complex cargo systems afloat. 

LPG (liquefied petroleum gas) carriers transport propane, butane, and related gases, which liquify at much higher temperatures, either under pressure at ambient temperature (small pressurised carriers) or refrigerated to −48°C at near-atmospheric pressure (large fully refrigerated carriers). 

The temperature difference between −162°C and −48°C represents a fundamental engineering distinction between the two vessel types.

Conclusion

The tanker industry moves the liquid foundations of the global economy, crude oil, refined fuels, chemicals, and gases across every corner of the world. Understanding how these vessels are classified is the starting point for understanding how that movement works, who operates it, and why the decisions made at the design and chartering stages reverberate through supply chains on every continent.

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