What Is Bunkering in Shipping?
Bunkering refers to the process of supplying fuel — commonly called bunker fuel — to a ship for use in its main propulsion engines, auxiliary engines, and onboard boilers. The term originates from the coal “bunkers” used to store fuel on early steam vessels.
Today, bunker fuel includes a range of products such as Heavy Fuel Oil (HFO), Marine Gas Oil (MGO), Very Low Sulfur Fuel Oil (VLSFO), Liquefied Natural Gas (LNG), and increasingly, alternative fuels like methanol and ammonia.
With the IMO’s 2020 sulfur cap and accelerating decarbonization targets under the IMO 2050 strategy, the choice of bunkering method and fuel type has become strategically vital for shipowners, operators, and port authorities alike.
“Fuel costs represent up to 60% of a vessel’s total operating expenditure — making bunkering decisions one of the most impactful choices in maritime commerce.”
The 6 Main Types of Bunkering
Bunkering methods vary based on the vessel’s location, port infrastructure, fuel type, and delivery volume. Below are the six primary types of bunkering operations used globally today.
Ship-to-Ship (STS) Bunkering
Ship-to-ship (STS) bunkering involves the direct transfer of fuel between two vessels — typically a bunker tanker and the receiving ship — while both are at anchor, at sea, or in a sheltered waterway. This method is widely used where port facilities are unavailable or when the receiving vessel is too large to berth.
STS bunkering is common in locations like the Strait of Malacca, the English Channel, and the Gulf of Mexico, where large vessels take on fuel before or after port calls to optimize their port turnaround times.
- No port required — flexible location
- Suitable for very large vessels (VLCC, ULCC)
- Can be performed while underway
- Reduces port turnaround time
- Weather and sea-state dependent
- Requires precise vessel coordination
- Higher spill risk than shore-based methods
- Complex regulatory compliance
Truck-to-Ship Bunkering
Truck-to-ship bunkering involves road tanker trucks delivering fuel directly to a vessel docked at a berth or pier. It is one of the most accessible and flexible bunkering options, particularly for smaller vessels, ferries, offshore support vessels, and yachts.
This method is popular in smaller ports and marinas that lack the infrastructure for pipeline or barge delivery, and it offers the advantage of relatively quick mobilization.
- Widely available — even in small ports
- Cost-effective for small quantities
- Fast mobilization time
- Suitable for multiple fuel grades
- Slow delivery rate (limited volume)
- Not practical for large commercial vessels
- Road access to berth required
- Traffic and logistics complexity
Shore-to-Ship (Pipeline) Bunkering
Shore-to-ship bunkering — also called pipeline bunkering — delivers fuel from onshore storage tanks through a network of fixed pipelines and hose connections directly to a vessel at berth. This is the most efficient high-volume delivery method and is the preferred option at major global bunkering hubs.
Key bunkering ports such as Singapore, Rotterdam, Fujairah, and Houston rely heavily on pipeline infrastructure to service tens of thousands of vessel calls per year.
- Highest delivery flow rates
- Accurate custody transfer metering
- Minimal weather risk
- Lower spill risk than STS
- Requires major port infrastructure
- Not available at smaller ports
- Vessel must berth at specific terminal
- High capital cost to install
Barge-to-Ship Bunkering
Barge-to-ship bunkering is the most common delivery method globally. A dedicated bunker barge — essentially a floating fuel tanker — travels out to the receiving vessel at anchor or alongside at berth and transfers fuel via hoses. This method is widely used in ports like Singapore (the world’s largest bunkering hub), Rotterdam, and Antwerp.
Bunker barges typically carry between 500 and 5,000 metric tonnes of fuel, and operations are coordinated through detailed scheduling and port authority oversight.
- Serves vessels at anchor or berth
- High volume capacity
- Flexible scheduling
- No fixed terminal infrastructure needed
- Barge availability and scheduling delays
- Weather and tidal conditions
- Potential for quantity disputes
- Barge fleet maintenance costs
LNG Bunkering
Liquefied Natural Gas (LNG) bunkering is one of the fastest-growing segments of the marine fuel supply industry. LNG is stored and transferred at cryogenic temperatures (approximately −162°C) and can be delivered via ship-to-ship, barge-to-ship, or truck-to-ship methods using specialized cryogenic equipment.
LNG dramatically reduces sulfur oxide (SOx) emissions by nearly 100%, nitrogen oxide (NOx) by up to 85%, and carbon dioxide (CO₂) by around 20–25% compared to conventional HFO. Leading LNG bunkering hubs include Rotterdam, Singapore, Barcelona, and major US East Coast ports.
- Major SOx/NOx/CO₂ reduction
- IMO 2020 compliant
- Growing global infrastructure
- Supports decarbonization targets
- Cryogenic equipment required
- Limited port availability vs. conventional fuel
- Higher vessel CAPEX for dual-fuel engines
- Methane slip concerns
Alternative Fuel Bunkering
As the maritime industry charts a course toward net-zero by 2050, alternative fuel bunkering is rapidly evolving. The primary candidates are methanol, green ammonia, hydrogen, and biofuels — each offering distinct emissions profiles and infrastructure challenges.
Methanol is already being used commercially by Maersk’s green methanol fleet. Ammonia is considered a strong candidate for deep-sea shipping due to its zero-carbon combustion, though toxicity handling remains a challenge. Green hydrogen offers the cleanest profile but faces significant energy density and storage hurdles. Biofuels (B20, B100) represent a near-term drop-in solution that can blend with existing fuel systems.
- Net-zero or very low lifecycle emissions
- Biofuels are drop-in compatible
- Aligned with IMO 2050 targets
- Growing regulatory support
- Immature global supply chains
- Higher cost vs. conventional fuel
- Engine/infrastructure modifications needed
- Safety/toxicity handling (ammonia)
Bunkering Methods: Quick Comparison
The table below compares the key attributes of each bunkering method to help operators make informed decisions.
| Method | Volume Capacity | Flexibility | Infrastructure Need | Best For |
|---|---|---|---|---|
| Ship-to-Ship | High | Very High | None required | Large vessels, offshore |
| Truck-to-Ship | Low | Medium | Minimal | Small vessels, yachts |
| Shore-to-Ship | Very High | Low | Extensive | Major hubs, high volume |
| Barge-to-Ship | Medium-High | High | Moderate | Most vessel types |
| LNG | Medium | Growing | Specialized | LNG-ready vessels |
| Alternative Fuels | Emerging | Limited | Very specialized | Future-ready vessels |
How to Choose the Right Bunkering Method
Selecting the appropriate bunkering method requires careful evaluation of several factors. Port location and available infrastructure are often the primary constraints — a vessel calling at a remote anchorage will not have the luxury of pipeline delivery. Volume requirements also play a decisive role; high-volume bunkering at a major hub almost always favors shore-to-ship or barge delivery for efficiency.
Regulatory compliance is increasingly important. The IMO’s MARPOL Annex VI regulations, the 2020 global sulfur cap, and Carbon Intensity Indicator (CII) ratings are pushing operators toward lower-emission fuel types and, by extension, specialized bunkering methods. Cost considerations must account for not just the fuel price but also the delivery premium, port dues, and any vessel modifications needed to accommodate new fuel types.
Finally, safety and environmental risk assessments — including spill response planning and crew training — must be factored into every bunkering decision, regardless of method.
Key Bunkering Regulations to Know
Bunkering operations are governed by a complex web of international, regional, and local regulations. The most significant include MARPOL Annex VI (air pollution and fuel quality standards), the IMO 2020 sulfur cap limiting marine fuel sulfur content to 0.5%, SOLAS regulations covering safe fuel handling procedures, and MAS regulations in Singapore governing bunkering operations within its port limits.
Operators bunkering with alternative fuels must also comply with emerging guidelines under the IGF Code (International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels), which is already mandatory for LNG-fueled vessels and is being expanded to cover methanol and ammonia.