Complete glossary of tanker, oil shipping, and maritime terms. From AIS to VLCC — everything you need to understand global tanker tracking.
A crude oil tanker with a deadweight tonnage (DWT) between 200,000 and 320,000 tonnes. VLCCs are the workhorses of long-haul crude oil trade, typically operating on routes from the Persian Gulf to East Asia and from West Africa to Europe. They can carry approximately 2 million barrels of crude oil.
The largest class of oil tanker, with a DWT exceeding 320,000 tonnes. ULCCs are rare in modern shipping due to port draft restrictions and the decline of very long-haul routes. Most have been scrapped or converted.
A tanker sized to transit the Suez Canal fully laden, typically 120,000–200,000 DWT. The name refers to the maximum size that can pass through the canal. Suezmaxes are versatile vessels used on medium-haul routes, including West Africa to Europe and the Mediterranean to Asia.
A medium-sized tanker of 80,000–120,000 DWT. The name derives from the Average Freight Rate Assessment (AFRA) system used by Shell. Aframaxes are the most common tanker size, ideal for ports with draft limitations and shorter routes such as the North Sea, Mediterranean, and Caribbean.
A vessel sized to fit through the original Panama Canal locks, typically 60,000–80,000 DWT. After the canal expansion in 2016, the term "Neopanamax" refers to larger vessels that can transit the new locks (up to ~120,000 DWT for tankers).
A specialized tanker designed to transport liquefied natural gas at approximately −162°C. Modern LNG carriers typically have a capacity of 125,000–180,000 cubic metres. They use either membrane-type (GTT) or spherical (Moss-type) containment systems. Some newer vessels use LNG as fuel (dual-fuel engines).
A tanker designed to carry liquid chemicals in bulk. Chemical tankers have specialized coatings (stainless steel, epoxy, zinc) in their cargo tanks to handle corrosive or reactive substances. They are classified as IMO Type 1, 2, or 3 based on the hazard level of cargo they can carry.
A floating vessel used for offshore oil production, storage, and transfer. FPSOs are moored at oil fields, process crude oil from subsea wells, store it onboard, and periodically offload to shuttle tankers. They are essentially floating oil platforms combined with storage tankers.
The total weight a vessel can carry, including cargo, fuel, crew, provisions, and ballast water. Measured in metric tonnes. DWT is the primary measure of a tanker's carrying capacity. A VLCC has roughly 300,000 DWT, meaning it can carry 300,000 tonnes of total load.
A measure of a ship's total internal volume, not weight. One gross ton equals 100 cubic feet (2.83 m³). GT is used for port fees, canal tolls, and safety regulations. Not to be confused with DWT, which measures carrying capacity by weight.
The maximum length of a vessel measured from the foremost point of the bow to the aftermost point of the stern. LOA determines whether a ship can enter certain ports, canals, or dry docks. A typical VLCC has an LOA of about 330 metres.
The width of a vessel at its widest point. Together with draft and LOA, beam determines a ship's ability to transit canals and enter ports. A VLCC typically has a beam of about 58–60 metres.
The vertical distance between the waterline and the bottom of the hull (keel). Draft increases when a vessel is loaded and decreases when empty. Maximum draft determines which ports and waterways a tanker can access. The Strait of Malacca has a draft limit of about 20 metres.
A vessel carrying cargo. A laden tanker sits lower in the water due to the weight of its cargo. On TankerMap, laden tankers are identified by their deeper draft and destination patterns (heading toward discharge ports).
A vessel sailing without cargo, carrying seawater in its tanks for stability. Ballast voyages typically follow cargo discharge — the tanker returns empty to a loading port. Ballast water management is regulated by the IMO to prevent spread of invasive species.
The transfer of cargo between two vessels moored alongside each other at sea or at anchor. STS operations are common for crude oil (lightering VLCCs in shallow ports) and increasingly scrutinized in the context of sanctions evasion, where tankers transfer cargo to obscure the origin of oil.
The process of transferring cargo from a large vessel to a smaller one to reduce draft, allowing the large vessel to enter shallow ports. Common with VLCCs that cannot enter many ports fully laden. Lightering zones exist off the coast of Texas (LOOP), Singapore, and other regions.
Unrefined petroleum extracted from the ground. Major crude oil benchmarks include Brent (North Sea), WTI (US), Dubai/Oman (Middle East), Urals (Russia), and ESPO (Russia Pacific). Crude is transported by tanker from producing regions to refineries worldwide.
A narrow waterway that concentrates maritime traffic into a confined passage. Chokepoints are strategically significant because disruptions (military conflict, piracy, natural disaster) can affect global oil supply. The world's most important oil chokepoints are the Strait of Hormuz, Strait of Malacca, Suez Canal, Bab el-Mandeb, Gibraltar, and the Panama Canal.
A routing system established by the IMO to separate opposing flows of vessel traffic in busy or confined waters. A TSS typically consists of traffic lanes separated by a separation zone. Major TSS areas include the Strait of Hormuz, Strait of Dover, and approaches to busy ports.
The passage of a vessel through an artificial waterway such as the Suez Canal or Panama Canal. Canal transits require booking, payment of tolls (based on vessel size), and often the use of local pilots. Transit times vary: Suez takes about 12–16 hours, Panama about 8–10 hours.
The market for chartering tankers for single voyages at current market rates. Spot rates fluctuate based on supply and demand — more available tankers means lower rates. Spot rates are quoted in Worldscale (WS) points or as a flat USD rate per tonne.
A contract where a shipowner leases a vessel to a charterer for a fixed period (months to years). The charterer pays a daily hire rate and covers voyage costs (fuel, port fees, canal tolls), while the owner covers operating costs (crew, maintenance, insurance). TC rates provide a more stable income than spot rates.
A standardised freight rate system for tanker voyages, published annually by the Worldscale Association. WS100 is the "flat rate" — a reference rate for each route. Actual spot rates are quoted as a percentage (e.g., WS65 means 65% of the flat rate). Higher WS numbers indicate higher freight costs.
Contango: when future oil prices are higher than spot prices, making it profitable to store oil in tankers for later sale (floating storage). Backwardation: when future prices are lower than spot, discouraging storage. During deep contango, traders charter VLCCs as floating storage, temporarily reducing available shipping capacity.
A mechanism introduced in December 2022 by the G7, EU, and Australia that allows Russian oil to be transported using Western shipping, insurance, and financial services only if the oil is purchased at or below a set price ($60/barrel for crude). The price cap created a two-tier tanker market: compliant vessels using Western services and a growing shadow fleet operating outside the cap.
A specialized agency of the United Nations responsible for the safety, security, and environmental performance of international shipping. The IMO sets global standards including SOLAS (safety), MARPOL (pollution), and the Ballast Water Management Convention.
Inspections carried out by national authorities on foreign-flagged vessels visiting their ports. PSC inspectors verify compliance with international safety and environmental standards. Vessels with deficiencies may be detained until problems are corrected. PSC inspection records are available through Equasis.
An independent organization that sets and verifies technical standards for ship construction and maintenance. Major classification societies include DNV (Norway), Lloyd's Register (UK), Bureau Veritas (France), and ClassNK (Japan). Class societies conduct regular surveys and issue certificates confirming a vessel meets safety standards.
A mutual insurance association that provides liability coverage to shipowners. P&I covers third-party risks including crew injury, cargo damage, oil pollution, and wreck removal. The International Group of P&I Clubs covers about 90% of the world's ocean-going tonnage. Western P&I coverage is restricted for vessels carrying Russian oil above the price cap.