#98 - Oil Tankers

Recent news in maritime shipping, geopolitics, and energy markets have put oil tankers back at the centre of attention.

Yet beyond the headlines, I think that they remain poorly understood pieces of (vital) infrastructure for human beings.

This week I wanted to take a direct look at how oil tankers actually work, the core technology onboard, what they require to operate, and how a typical journey runs from port to port.

General Information

Each year, oil tankers move roughly 2–3 billion tonnes of crude oil and refined products, accounting for around one-third of global seaborne trade by volume.

This traffic translates into billions of nautical miles sailed annually, with the vast majority of voyages completed without incident. Despite their scale and risk profile, serious tanker accidents are rare: major oil spills have fallen by over 90% since the 1970s, and in recent years typically fewer than 10 large spills (>700 tonnes) are recorded globally per year.

The reliability of tanker transport is one reason it remains essential, shipping oil by sea is still the lowest-cost and most energy-efficient way to move large volumes over long distances, underpinning electricity generation, transport fuels, petrochemicals, and heating systems worldwide.On an annual basis, oil tankers service roughly 15–20% of total global primary energy demand.

The Tech Stack of an Oil Tanker

Oil tankers are built as long-life industrial assets. Most are designed to operate for 20–25 years, running almost continuously, across different oceans, ports, and regulatory regimes. The technology onboard reflects that priority: reliability, safety, and scale.

Build, materials, and timelines

• Constructed primarily from high-grade steel, often 40,000–80,000 tonnes depending on vessel size

• Typical build time: 18–36 months from keel laying to delivery

• Built in large commercial shipyards, with design standardisation to simplify maintenance and inspections

Propulsion and power

• Powered by a single slow-speed two-stroke diesel engine

• Main engine output commonly ranges from 10–30+ MW

• Designed to run efficiently at constant speeds over long distances

• Auxiliary generators provide electricity for pumps, navigation, lighting, and onboard systems

Fuel consumption is significant:

• A large crude carrier can burn 60–100+ tonnes of fuel per day at sea, depending on speed and load

• Even small efficiency gains translate into large cost and emissions impacts

Cargo storage and handling

• Cargo is stored in segregated steel tanks, coated to prevent corrosion

• Total cargo capacity ranges from:

  • ~30,000 tonnes (product tankers)

  • up to 300,000+ tonnes (very large crude carriers)

• Loading and discharge rely on high-capacity pump systems moving thousands of cubic metres per hour

• Continuous monitoring of pressure, temperature, and tank levels is standard

Navigation and control

• Bridge systems combine:

  • GPS positioning

  • Radar and collision avoidance

  • Electronic charts and route planning

• These systems prioritise redundancy, failure is not an option mid-ocean

Safety and compliance systems

• Inert gas systems reduce explosion risk inside cargo tanks

• Fire detection and suppression systems are built into cargo and engine spaces

• Ballast water treatment systems manage vessel stability while meeting environmental rules

Overall, oil tanker technology is optimised for scale, durability, and risk control, moving vast quantities of hazardous cargo safely, repeatedly, and predictably across the globe.

Ports, Cargo Turnaround, and the Journey Lifecycle

Once an oil tanker is built, most of its value is realised through repeated port-to-port cycles. Time in port is expensive, tightly controlled, and heavily regulated.

Fun fact: In certain market conditions, oil tankers are deliberately held at sea as floating storage to wait out price changes, but this is costly and only occurs when price signals are strong enough to justify keeping vessels idle rather than moving cargo to port. In April 2020, for example, an estimated 150–200 million barrels of oil were stored at sea globally.

Before arrival

• Voyage planning starts days in advance, factoring in weather, port congestion, tides, and berth availability

• Tankers coordinate with terminals, pilots, and port authorities

• Documentation is prepared for cargo, safety, customs, and environmental compliance

Loading at the export terminal

• Loading crude oil or products typically takes 12–48 hours, depending on cargo size and terminal capacity

• High-capacity pumps move thousands of cubic metres per hour through fixed loading arms

• Continuous monitoring checks tank levels, pressure, temperature, and vapour control

• Safety procedures dominate: grounding, gas checks, emergency shutdown readiness

Transit at sea

• Voyages commonly span 5–40+ days, depending on route and vessel size

• At sea, the focus is on:

  • Steady engine operation

  • Fuel efficiency and speed optimisation

  • Navigation and collision avoidance

  • Regular reporting to operators, charterers, and regulators

• Even while sailing, tankers generate large volumes of operational and compliance data

Discharge and turnaround

• Discharging mirrors loading but often takes longer due to terminal constraints

• After discharge:

  • Tanks may be cleaned or prepared for the next cargo

  • Inspections are carried out

  • Ballast is adjusted for stability

• Total port turnaround can range from 1–4 days, but delays are common and costly

Across a year, a single large tanker may complete 6–10 full voyages, with profitability driven less by speed and more by minimising downtime, avoiding incidents, and staying compliant. The journey lifecycle is repetitive, procedural, and highly optimised, leaving little room for error, but limited room for experimentation as well.

Concluding remarks

Oil tankers remain some of the most critical, and least examined, assets in the global energy system. Their technology is built around scale, reliability, and risk control, while their journeys are shaped by tight port operations, regulation, and market signals rather than constant innovation.

Understanding how these vessels actually operate is a necessary starting point for any conversation about safety, efficiency, digitalisation, or decarbonisation in maritime energy transport.

Viva Venezuela!

OTI-H