1. What is AIS and How Does It Work?
The Automatic Identification System (AIS) is a maritime tracking technology required by the International Maritime Organization (IMO) on all vessels over 300 gross tonnage engaged in international voyages. Every tanker broadcasts its position, speed, heading, and identity via VHF radio signals every few seconds.
These signals are received by coastal stations and satellites, creating a global network of vessel tracking data. AIS data includes:
- Static data (set once): IMO number, MMSI, vessel name, ship type, dimensions
- Dynamic data (updated continuously): latitude/longitude, speed over ground (SOG), course over ground (COG), heading, navigation status
- Voyage data (entered by crew): destination, ETA, draught
TankerMap collects AIS data from multiple sources to provide comprehensive coverage of the global tanker fleet.
2. Understanding Tanker Types and Sizes
Oil tankers are classified by their deadweight tonnage (DWT) — the maximum weight they can carry. Knowing these categories helps you understand global trade patterns:
- VLCC (Very Large Crude Carrier): 200,000–320,000 DWT. The backbone of long-haul crude trade. Routes: Persian Gulf → Asia, West Africa → Europe/Asia.
- Suezmax: 120,000–200,000 DWT. Named for the maximum size that can transit the Suez Canal fully laden. Common on Black Sea, West Africa, and North Sea routes.
- Aframax: 80,000–120,000 DWT. Versatile tankers for medium-haul routes. Common in the Baltic, Mediterranean, Caribbean, and Southeast Asia.
- Panamax: 60,000–80,000 DWT. Sized for the old Panama Canal locks. Used for refined products and smaller crude cargoes.
- LNG Carrier: Specialized vessels carrying liquefied natural gas at -162°C. Sizes from 125,000 to 270,000 m³.
On TankerMap, you can filter vessels by type to focus on specific segments of the fleet. See our Glossary for detailed definitions of each type.
3. Reading Vessel Data on the Map
When you click on a vessel marker on TankerMap, you'll see key information:
Position & Movement: - Current coordinates (latitude, longitude) - Speed over ground (SOG) in knots — 0 means anchored or moored - Course over ground (COG) — direction of travel in degrees - Navigation status — "Under way", "At anchor", "Moored"
Vessel Identity: - Name and IMO number (unique lifetime identifier) - MMSI (radio identifier, can change with flag) - Flag state — country of registration - Vessel type and size class
Voyage Info: - Destination — the port the crew has entered as their next stop - ETA — estimated time of arrival - Draught — how deep the hull sits in water (indicates cargo load)
What draught tells you: A VLCC with a draught of 20+ meters is likely fully laden with crude oil. The same vessel at 8-10 meters is in ballast (empty, returning for the next cargo). This is how analysts determine whether tankers are carrying oil.
Click the vessel name to open its full profile page with detailed specifications, current voyage, and historical track.
4. Key Chokepoints: Where to Watch
Maritime chokepoints are narrow waterways through which a significant share of global oil passes. Monitoring tanker traffic through these points reveals supply disruptions, trade shifts, and geopolitical risks:
- Strait of Hormuz — ~21 million barrels/day. The world's most critical oil chokepoint, connecting the Persian Gulf to the Arabian Sea. About one-third of all seaborne oil passes here.
- Strait of Malacca — ~16 million barrels/day. Links the Indian Ocean to the Pacific, vital for oil flowing to China, Japan, and South Korea.
- Suez Canal — ~9 million barrels/day. Connects the Mediterranean to the Red Sea. Disruptions (like the 2021 Ever Given incident) cause global supply chain delays.
- Bab el-Mandeb — ~6 million barrels/day. Links the Red Sea to the Gulf of Aden. Houthi attacks since late 2023 have diverted traffic around the Cape of Good Hope.
- Strait of Gibraltar — Gateway between the Atlantic and Mediterranean.
- Panama Canal — ~1 million barrels/day. Drought-related restrictions have limited transits since 2023.
TankerMap tracks real-time tanker transits through all six major chokepoints. Visit our Analytics page for live counts and historical charts.
5. Laden vs Ballast: Is the Tanker Carrying Oil?
One of the most valuable pieces of information in tanker tracking is whether a vessel is carrying cargo (laden) or traveling empty (in ballast).
How to tell: - Draught: The most reliable indicator. A laden VLCC sits 20-22 meters deep; in ballast, only 8-10 meters. - Speed: Laden tankers often sail slower (12-13 knots) than ballast tankers (13-15 knots) to save fuel. - Route direction: A tanker heading from the Persian Gulf toward Asia is likely laden. The same vessel returning from Asia to the Gulf is likely in ballast.
TankerMap shows laden/ballast status on vessel markers and lets you filter the map to show only laden or only ballast tankers — useful for tracking actual oil flows vs. repositioning movements.
6. The Dark Fleet: Tankers That Go Silent
The "dark fleet" refers to tankers that deliberately disable or manipulate their AIS transponders to avoid detection. This practice has grown significantly since 2022, primarily linked to sanctions evasion on Russian, Iranian, and Venezuelan oil exports.
Signs of dark fleet activity: - AIS gaps: Extended periods (6+ hours) with no position data - Flag changes: Frequent re-flagging to obscure ownership - Old vessels: Average age 15-20+ years, often uninsured by Western P&I clubs - Ship-to-ship (STS) transfers: Cargo transferred at sea to obscure origin - Unusual routes: Deviations or loitering in open ocean
Scale: Estimated 600-800 tankers operate in the dark fleet as of 2025-2026, carrying millions of barrels daily outside the Western-monitored system.
TankerMap's Sanctions page flags vessels on international sanctions lists. Visit the Fleet page to explore the global tanker fleet.
7. Start Tracking on TankerMap
Ready to explore? Here's how to get started:
1. Open the Map — Visit tankermap.com to see all tracked tankers worldwide in real time. 2. Filter by type — Use the filter panel to show only VLCCs, Suezmax, or LNG carriers. 3. Search a vessel — Enter a vessel name or IMO number in the search bar. 4. Explore Analytics — Check Analytics for chokepoint transit counts and port statistics. 5. Read the News — Stay informed with our News section covering tanker market developments. 6. Check the Fleet — Browse the complete Fleet directory by operator.
TankerMap is free and requires no registration. All data updates in real time.