Material Insights · Understanding the Material World

Tankers, barges and fuel trucks: How it works

How a floating steel box carries two million barrels safely

What this tab covers How the energy actually moves, step by step: the science that makes it work and the engineering that makes it practical.

About three-quarters of the world's oil travels by sea, mostly in tankers: floating steel hulls divided into tanks. On land and rivers, rail tank cars, road tankers and barges cover the rest, and in war zones drums, cans and refuelling aircraft.

Step by step

  1. Load at a terminalShore pumps fill the separate cargo tanks (a typical VLCC has 17), measured by tank gauges and shore meters.
  2. Make the tanks safeInert gas from cleaned exhaust fills the space above the oil, keeping oxygen too low for fire.
  3. SailA loaded VLCC draws about 20 m and passes chokepoints such as Hormuz, Malacca, Bab el-Mandeb and Suez, or rounds the Cape.
  4. DischargeSteam-driven cargo pumps push the oil ashore while inert gas refills the tanks so they do not buckle.
  5. Onward and last mileFuels move on by product tanker, barge, rail or road tanker. Armies add convoys, jerrycans and aircraft that refuel others in flight.

The science

A ship floats by pushing aside its own weight of water (Archimedes' principle). Double a hull's length, width and depth and it holds about eight times the cargo with only about four times the wetted surface, so drag per tonne falls as ships grow: that is why supertankers exist. Propulsion power rises roughly with the cube of speed, so slowing down saves fuel steeply. Keeping tank oxygen low removes one side of the fire triangle (fuel, oxygen, heat).

The engineering

VLCCs (very large crude carriers) are 200,000 to 300,000 deadweight tonnes and about 340 m long; Suezmax and Aframax ships are smaller. Product tankers have coated or stainless tanks so cargoes stay clean. Modern tankers have double hulls and inert gas systems. US rail tank cars for flammable liquids are moving to the DOT-117 design (thicker steel, head shields, thermal jacket), and road tankers use baffled compartments.

Key numbers

Seaborne oil trade (first half 2025) 79.8 million b/d, about 76% of world oil supply1 VLCC cargo about 300,000 to 320,000 tonnes, roughly 2.2 million barrels (calculated)3 VLCC round trip, Middle East to Japan about 50 days including loading and discharge3 US rail tank cars in flammable liquid service (2025) 100,485, of which 76% were DOT-117 or 117R19 Strait of Malacca oil flow (first half 2025) 23.2 million b/d, the largest chokepoint1

Sources

  1. World Oil Transit Chokepoints (last updated 3 March 2026) US EIA, 2026
  2. From our vessels around the world: VLCC NYK Line, 2025
  3. Phaseout deadline for older tank car types passes as the number of safer tank cars continues increasing (2026 Tank Car Report) US Bureau of Transportation Statistics, 2026