Bunkering

Bunkering refers to the process of refuelling a ship. To ensure safe and efficient operations, this process must follow standardised protocols, such as those outlined in ISO 13739, which ensure consistency and reliability in operations.

The term “bunker” refers to the fuel used to power ships, and a “bunker trader” is the key player who handles its sale and distribution. Ships are typically refuelled using one of four primary bunkering methods, which are detailed below.

Types of Bunkering Operations: Stern-Line Bunkering

Ship-to-ship (STS) bunkering is one of the most widely used methods for refuelling ships. In this method, one vessel transfers fuel directly to the other. The two ships position side by side, typically at designated bunkering terminals. The supplying vessel pumps fuel through manifolds, loading arms, or flexible hoses. This method is highly efficient, particularly for large-scale fuel transfers, offering seamless access to the ship’s fuel intake points. It’s especially ideal for meeting the fuelling demands of larger maritime vessels.

Key steps in the STS procedure include checking the compatibility and positioning of both vessels, ensuring they are perfectly aligned. Next, a detailed fuel transfer plan is created to keep everything on track. Crew members then securely moor the ships together, followed by the careful connection of the cargo hose. To prevent any issues, operators cool down the hose, pipelines, and tanks. Throughout the process, the crew must control the fuel flow, monitor weather conditions, and check the stratification of the fuel to maintain quality and safety at all times.

Types of Bunkering Operations: Stern-Line Bunkering

Stern-line bunkering involves transferring fuel from the stern of the bunker vessel to a trailing ship. This technique is particularly valuable when side-by-side berthing isn’t possible, such as in confined harbours or during rough sea conditions. It demands precise vessel alignment and seamless coordination, as the fuel hose extends from the rear of the supplying vessel to the intake point of the receiving ship.

Types of Bunkering Operations: Onshore-to-Ship Bunkering

Onshore-to-ship bunkering uses pipelines that link an onshore fuel storage facility directly to the vessel. This method is particularly well-suited to vessels with high fuel demands. Flexible hoses carry out the transfer, typically at a dedicated bunkering terminal. Major global ports such as Singapore, Rotterdam, Fujairah, and Houston commonly use this approach.

Types of Bunkering Operations: Truck-to-Ship Bunkering

Truck-to-ship bunkering is the go-to method when flexibility and on-the-spot delivery are needed. With this approach, tanker trucks transport and pump fuel directly to the ship. It’s especially useful for smaller vessels or short-term refuelling needs, offering quick setup, lower initial costs, and minimal maintenance requirements. However, because trucks carry limited volumes, this method isn’t suitable for large-scale operations or fuelling larger ships.

What is the Preferred Bunkering Method?

An analysis of operator perspectives reveals a clear preference for the onshore-to-ship bunkering method, with truck-to-ship and ship-to-ship following in rank. When deciding what bunkering methods to use, operators must weigh critical factors in the following order: safety, economic feasibility, technical requirements, and operational considerations.

The various types of fuel used and transferred during bunkering operations for vessels over 5,000 GT are detailed:

• Low Sulphur Fuel Oil (LSFO) / Light Fuel Oil (LFO): Engineered to meet strict environmental standards, these fuels contain reduced sulphur levels to help reduce air pollution from ships.
• High Sulphur Fuel Oil (HSFO) / Heavy Fuel Oil (HFO): With a higher sulphur content, this fuel is typically used in areas with less stringent emissions regulations.
• Low Sulphur Marine Gas Oil (LSMGO): Known for its clean burn and ultra-low sulphur content, LSMGO is a preferred option for emission control areas.
• Marine Diesel Oil (MDO) / Gas Oil: A blended fuel combining distillate and residual components, MDO is widely used in medium- to low-speed diesel engines.
• Liquefied Natural Gas (LNG): A cryogenically liquefied fuel, primarily composed of methane, offering low-emission combustion. It requires specialised engines and advanced bunkering systems due to its extremely low storage temperatures.
• Ethanol: Produced from biomass, ethanol is a renewable fuel option that supports cleaner combustion. It requires specially designed engines and bunkering systems for safe and effective marine use.
• Ammonia: Ammonia is emerging as a viable zero-carbon marine fuel, meaning it has the potential to significantly reduce greenhouse gas emissions. It benefits from an established global production and transport infrastructure, although safety and handling remain key challenges.
• Hydrogen: Hydrogen presents a clean energy solution for the shipping industry, producing only water when used in fuel cells. However, its low energy density and complex storage requirements present significant technical and economic hurdles.
• Methanol: Methanol is a low-carbon fuel that can be produced from both fossil-based and renewable sources, making it a flexible option for shipping. It is easy to store and handle, and can be used in modified conventional engines, enabling smoother industry adoption.

Maritime regulators strictly regulate bunkering to ensure the safe, efficient and compliant transfer of fuel from supplier to vessel.

Step 1: The Preparation Stage

Before any fuel transfer begins, the crew of the receiving ship prepares a detailed bunkering plan. This plan outlines the amount of fuel needed and exactly which tanks to fill.

Once the crew confirms the plan, the vessel docks at a supply ship offshore to begin the refuelling process.

Clear communication is critical from the outset. Both parties must convey operational steps, safety protocols, emergency signals, and current onboard fuel levels accurately.

As a safeguard, the crew keeps oil spill response gear on standby, ready to deploy immediately in the event of a leak or spill. Once they complete preparations, they connect the fuel hose and open the line valves. They keep the master valve closed until they finish a final round of safety checks, which include:

• Inspecting hoses, pumps, and all bunkering equipment;
• Ensuring fuel tanks are ready to receive fuel;
• Verifying that safety equipment such as handrails, ropes, and lighting is in place;
• Confirming all crew members involved are well-rested and alert.

A word of caution: Refuelling mid-voyage without prior approval may constitute a “deviation” – a serious breach of the shipping contract. This can result in legal and financial consequences, potentially violating agreements with insurers, cargo owners, or other stakeholders.

Worse still, if a ship runs out of fuel at sea, the consequences can be severe. Not only could the vessel lose insurance coverage, but cargo receivers might also file claims for damages. In extreme cases, salvors must tow the stranded vessel to safety, which is a costly operation.

Step 2: The Performance Stage

Before bunkering begins, the crew may need to relocate existing fuel from certain tanks to make room for the incoming supply. They must empty and clean these tanks to prevent any chemical incompatibility between the old and new fuel. The overflow tank must also be empty and ready to catch any excess, if necessary.

On deck, teams plug drip trays and scuppers to prevent accidental spills from reaching the sea. They also prepare spill response equipment, in line with the Shipboard Oil Pollution Emergency Plan (SOPEP), and keep it within immediate reach.

Throughout the operation, crew members use sounding measurements – manual checks with calibrated tapes or sticks – to monitor fuel levels in the tanks. Meanwhile, they record the ship’s draught and trim to ensure proper weight distribution, which is crucial for fuel efficiency during the voyage.

The Bunkering Process Begins

The crew officially begins the bunkering process by opening the manifold valve, allowing fuel to flow into the designated tanks. They pump the fuel slowly at first to detect any early signs of leaks or equipment faults. Once they confirm all systems are operating correctly, they increase the pumping rate to the agreed level.

Crew members must continuously monitor fuel levels. As a tank nears 90% capacity – the safe upper limit – they slow the pumping rate. When refilling more than one tank, they open the next set of valves to redirect the fuel. If refuelling only one tank, they carefully top it off. Once the tank reaches the desired level, the supervising officer orders the operation to stop and closes the master valve, marking the end of the transfer.

This stage requires tight coordination and constant communication. All crew members must follow the agreed bunkering plan precisely and strictly observe safety protocols. Key responsibilities include:

• Managing the fuel transfer in a controlled, step-by-step manner;
• Maintaining constant vigilance to respond immediately to any irregularities.
• Before signing off, the chief engineer inspects the operation. This includes checking the supplier’s documentation to verify that the fuel’s grade and density meet the required specifications.
• Monitoring fuel temperature is another critical task. Fuel expands when hot and contracts when cold. Failing to account for this can result in unexpected shortfalls later.

Step 3: Post-Transfer Stage

After finalising the bunkering process, the crew clears the pipeline of any remaining fuel by flushing it with compressed air.

They then carry out a final round of checks, including:

• Conducting safety inspections to confirm proper adherence to all procedures;
• Measuring tank levels, trim, and draught to verify that the correct type and volume of fuel has been received – adjusting for temperature, trim, and heel as required.

Once these checks confirm that the delivered fuel matches the original order, the bunkering process officially concludes. However, if they identify any discrepancies, the chief engineer may request additional fuel or negotiate fair compensation with the supplier.

When both parties agree that they have met all contractual and safety requirements, they sign the bunkering receipt. The crew also documents the operation fully for compliance and future reference.

The next critical step is fuel sampling. The crew collects four fuel samples to assess the quality of the delivered fuel:

• One sample goes to a laboratory for independent analysis.
• The ship, the bunker supplier, and the port authority each retain one sample.

The port authority’s sample plays a vital role in verifying compliance with international environmental standards, particularly those outlined under MARPOL Annex VI by the International Maritime Organization (IMO).

If all tests confirm that the fuel meets the required specifications, the crew disconnects the hose safely and clears the ship for departure.

New Insights: Key Bunkering Risk Management

Bunkering operations present considerable environmental risks and are vulnerable to fraud and deceptive practices. Discrepancies in fuel quantity and quality are also common concerns. To ensure safe and efficient operations, it is important to equip key stakeholders with the knowledge and skills to manage these risks effectively.

Although most bunkering operations go smoothly, even a single error can trigger serious environmental damage and safety hazards.

Manage bunkering proactively by conducting thorough risk assessments and implementing clear procedures. Put a comprehensive bunker plan in place that identifies and addresses all potential risk scenarios to maintain safety throughout the operation.

Bunker Planning Checklist

You should prepare a bunker plan that includes the following components:

A precise overview of the types and quantities of fuel to be delivered.

A detailed plan showing which bunker tanks will be used, including the type and quantity of fuel for each tank, as well as their maximum allowable filling limits.

A diagram of the vessel’s bunker system, highlighting correct valve configurations.

A step-by-step filling sequence and the required pumping rates, specifying the initial flow rate, peak flow rate, and topping-off rate.

Clear guidelines on the safety margin (or slack space) in each tank, for example, ensuring no tank exceeds 90% capacity.

Soundings of each tank before bunkering begins, along with the expected soundings or ullages upon completion of the operation.

The method you will use for taking soundings or ullages to avoid misunderstandings.

The identification of the person in overall charge of the operation (typically the Chief Engineer), and the roles and responsibilities of other personnel involved.

The emergency procedures and contact information.

A procedure for draining and blowing through the lines once bunkering is complete.

Specified flushing volumes and methods if the same pipeline is used for different fuel grades.

Verification or testing procedures of high-level alarm settings in the fuel tanks, or an alternative method if alarms are not provided.

The proper labelling and clear identification of all bunker line valves.

Instructions for switching between tanks during the bunkering process.

Consideration of vessel stability, including draught, trim, and list at various stages of the operation.

Adequate manning to ensure the entire operation is conducted safely and efficiently.

Before the bunkering operation begins, the Chief Engineer should gather the team for a ‘toolbox talk’, bringing together personnel from both the Deck and Engineering departments. This is a vital opportunity to walk everyone through the bunker plan, ensuring each person fully understands not just the steps involved but their responsibilities in carrying out the operation safely.

During this briefing, crew members must follow the bunkering checklist and review risk assessments to confirm that all safety controls are firmly in place. Assign only crew members who are well‑versed in the ship’s bunkering systems and procedures.

For new team members, pairing them with an experienced crew member is key. This hands-on mentorship helps build their confidence and knowledge while ensuring the entire operation runs smoothly and safely.

Pre-Bunkering Checks

When the bunker barge arrives, the responsible engineer and the barge master must meet without delay to align on the upcoming operation. This meeting plays a crucial role in securing a safe and smooth fuel transfer, and should cover the following key points:

Review and update bunkering procedures, checklists, and risk assessments regularly.

Ensure all documents are accurately completed and followed before starting any bunkering operation.

Confirm all bunker types being supplied, including grades, densities, and quantities.

Check and verify soundings and ullages of all fuel tanks on both the barge and the vessel.

Inspect SOPEP equipment to ensure it is in good condition and readily available.

Confirm that regular oil spill response drills have been conducted.

Ensure oil spill response equipment is in a ready state before bunkering.

Ensure the Chief Engineer and Engineer Officer of the Watch have verified all control measures.

Confirm that all blank flanges on the bunker manifold are in place and all valves are closed.

Ensure pressure gauges are installed and operational.

Ensure save-alls are clean and fit for purpose, with drain plugs secured.

Ensure deck scupper plugs are maintained, fit for use, and securely in place.

Confirm all bunker tank valve positions and double-check valve operations.

Check that bunker sounding pipes are closed or capped, and that air vents are inspected for blockages or damage.

Inspect the fuel oil overflow tank and sight glass; test flow and high-level alarms.

Confirm that fuel oil service tanks are filled, and purification equipment is switched off.

Prepare the bunker system and thoroughly double-check it to ensure:

The bunkering hose is in good condition.

Primary and backup communication systems are established between the vessel and the facility.

Emergency stop signals have been established and agreed upon.

The fire-fighting system is ready for immediate use.

The sampling point and method are agreed upon beforehand.

The relevant checklists are correctly completed and verified by both parties.

Mooring arrangements are secure and continuously monitored.

The loading hose is undamaged – verify certification if necessary.

Once the hose is connected, inspect the hose-to-manifold connection, ensuring the gasket is fitted and bolts are tightened.

Check surrounding waters for signs of existing pollution or hazards.

Confirm fire safety notices and equipment are posted, and international safety signals are displayed.

Bunkering Safety Checklist: Minimising the Possibility of an Oil Spill

To reduce the risk of an oil spill, or to minimise its impact, complete the following checklist:

Assign enough crew members to the ship’s bunkering team who are familiar with the system and procedures. A lack of adequately trained personnel has frequently contributed to spills, especially during tank topping-off.

Confirm that the valve on the receiving tank is open.

Check the capacity of the receiving tank.

Verify that the bunkering hoses are correctly connected and that the drip trays are properly positioned at the flanges.

Plug in all scrubbers.

Agree on the communication system with all parties involved.

Assign duty personnel from both parties.

Provide access to the necessary absorbent materials for dealing with accidental oil escapes.

Close exterior doors and portholes.

Position a portable chemical fire extinguisher near the manifold.

Close unused manifold valves and ensure connections are blanked and fully bolted.

Inspect bulkheads, pipelines, valves, and the hull for any leaks.

Check that ropes are in good condition.

Securely moor the vessel.

Confirm that the fenders are in good order and suitably positioned.

Inspect the cargo nets, lifting cages, strops, etc., to ensure they are in good condition.

Rig the transfer hose properly and fully bolt the flanges.

Regulate the environmental threshold for cargo operations according to the supplier’s guidelines. Clearly state the wind force scale at which bunkering must stop.

Start the bunkering operation at a low pumping rate. After confirming no leaks and proper flow, increase the rate to the agreed level. Check for leaks on both active and inactive manifolds, verifying that the fuel enters only the intended tanks.

Continuously monitor tank levels, including unused tanks, and adhere to agreed safety margins.

Keep accurate, timely records of pumping rates and regularly check gauges to maintain line pressures within safe limits.

Frequently inspect the sight glass and level of the bunker overflow tank.

Maintain ongoing checks on both primary and backup communication channels throughout the operation.

Regularly inspect mooring arrangements and remain vigilant for nearby passing traffic.

Routinely examine the manifold and hoses for leaks. If any drips occur, stop the operation immediately and rectify the issue before continuing.

Inspect bunker tank sounding pipes and vents regularly; keep sounding pipes closed and capped when not in use.

Change over tanks promptly, confirming adequate ullage and valve positions. Always open the receiving tank valve before closing the current one.

Continue monitoring completed tanks to confirm that valves are fully closed. When remotely operated valves are used, visual confirmation of their positions is recommended. Notify the bunkering facility and reduce the pumping rate when topping off, maintaining agreed safety margins.

Drain rainwater or other liquids from the deck to keep scuppers dry and prevent oil escaping overboard.

Minimise watch handovers; when necessary, make them thorough, accurate, and communicate the current status of the operation.

Coordinate the operation jointly with the barge crew, avoiding giving them sole control over the process.

Verify that the MARPOL drip sampler is working correctly and that required samples are taken. Double-check the delivered fuel temperature and conduct compatibility tests if necessary.

Remain alert throughout the bunkering operation. Investigate any unexpected changes or irregularities immediately and suspend the operation if in doubt.

Oil spills from bunkering activities represent one of the most significant environmental risks in maritime operations. These spills typically occur due to a loss of containment, such as tank overflows, pipeline leaks, or failures in transfer hoses.

Bunker spills pose two critical concerns:

• Long-term environmental damage to marine life and ecosystems.
• Legal repercussions for crew members and shipowners, which can include criminal prosecution.

Contrary to common belief, most oil pollution does not arise from oil carried as cargo, but from the release of bunker fuel.

Since 1970, over 80% of recorded oil spills have been small (under 7 tonnes), with bunkering operations accounting for 7% of these incidents. Between 2014 and 2018, bunker spills were responsible for 18% of all pollution incidents reported by Gard P&I Club, with the average cost per incident exceeding USD 100,000. Reports indicate that a significant portion of these spills occur during the transfer process.

Understanding the Causes of Oil Spills from Bunkering

To effectively reduce oil spills from bunkering operations, it is essential to pinpoint their root causes. A comprehensive 2021 study identified the key factors contributing to bunker oil pollution. These include:

• Crew Fatigue: Long working hours and pre-bunkering tasks can leave crew members exhausted, increasing the likelihood of lapses in attention and errors.
• Incompetent Crew: Inexperienced or undertrained personnel – often a result of minimal manning policies – can heighten operational risks.
• High Workload: Mechanical breakdowns and multitasking during bunkering increase pressure and the potential for mistakes.
• Inadequate Familiarisation: A lack of proper pre-operation briefings or poor handovers between shifts can lead to confusion and errors.
• Faulty Alarms and Sensors: Non-functional high-level alarms or inaccurate tank sensors may go unnoticed, resulting in overfills.
• Over-Reliance on Manual Checks: Inaccurate manual soundings, coupled with over-reliance on automated systems, can lead to errors.
• Incorrect Line-Up: Opening the wrong valve or incorrect line setups may direct fuel into a full tank.
• Poor Planning: Miscalculations in tank capacities or misinterpretation of sounding data can result in overflows.
• Onboard Communication Failures: Disruptions caused by noise, weather, or technical issues can hinder communication between crew members.
• Barge–Vessel Communication Gaps: Miscommunication or a lack of standard signals between the vessel and fuel barge can cause operational errors.
• Adverse Sea Conditions: Bunkering in rough seas – often under commercial pressure – can compromise safety and exacerbate risk.
• Tank Position Challenges: Tanks located in hard-to-monitor areas, such as double bottoms or sides, are more difficult to control, especially during high-speed transfers.
• Poor Flange Connections: Loose or improperly secured flanges can lead to leaks.
• Damaged Transfer Hoses: Worn or ruptured hoses during transfer operations are a direct source of spills.

The Study’s Key Findings

• The study revealed that tank overflow is the leading cause of oil spills during bunkering, raising the pollution risk from 4% to a staggering 95%.
• Operational issues (such as errors during the transfer process) increased the risk from 4% to 19.1%.
• Crew-related factors (like fatigue or a lack of experience) raised the risk by 8.7%.
• Inadequate monitoring and poor tank placement contributed to a 3.7% increase in risk.
• Communication breakdowns added 3.1%.
• Incorrect line-up resulted in a 2.3% rise in risk.
• Smaller contributors included malfunctioning alarms and damaged hoses (each increasing risk by 0.7%).
• Poor flange connections had the least impact, increasing risk by 0.5%.

Implications for Management

These findings highlight the crucial need to improve crew training, equipment maintenance, operational planning, and communication. By leveraging this knowledge, regulatory bodies, P&I Clubs, and shipowners can implement more effective risk mitigation strategies, significantly reducing the incidence of oil pollution during bunkering activities.

Technical Management: To reduce the risk of fuel overflows, tank design is critical. Storage tanks should have smooth, rectangular shapes and be located away from the ship’s curved hull areas for improved control. Overflow systems must be engineered to divert excess fuel safely into designated containment tanks – not onto the deck. These best practices reflect findings by Krata and Jachowski (2021), who identified flawed tank design as a major factor in spill incidents.

Crew Management: Regular training, hands-on exercises, and performance reviews are essential, particularly for newer or less experienced crew members. Investing in people is a direct investment in safety.

Maritime Education: Institutions must prioritise high standards in both theoretical knowledge and practical bunkering training to prepare graduates for the real-world challenges of fuel handling.

Commercial Management: The temptation to bunker in rough seas – whether due to charterer pressure or discounted fuel – comes with high risks. The cost of an oil spill, both environmental and financial, far outweighs any short-term savings. Safe operations must always come first.

How Podium by Pole Star Global Supports Safer Bunkering Operations

Pole Star Global’s Podium platform helps mitigate oil spill risks from bunkering operations by enabling proactive, data-driven decision-making, using:

• Advanced Weather Forecasting: Access high-resolution, route-specific forecasts to help avoid adverse sea conditions during bunkering.
• Dynamic Voyage Planning: Dynamically adjust bunkering plans and vessel routing based on live weather updates and sea conditions, minimising disruption and enhancing operational flexibility.
• Route Optimisation: Podium supports optimal port and anchorage choices for bunkering by evaluating weather risks, fuel efficiency, and regulatory compliance in real time.
• Operational Transparency: Easily share Podium insights with charterers and stakeholders to justify weather-related bunkering adjustments, reinforcing a safety-first approach and building trust.
• Centralised Decision Support: Leverage a centralised dashboard combining vessel location, weather forecasts, and regulatory overlays to enable faster, data-driven decisions during bunkering planning and execution.

Other Practical Considerations

Bunkering often takes place near coastlines – either at anchor or alongside the dock – where even small spills can cause immediate damage to fragile coastal ecosystems. Ports and operators should be prepared with rapid-response plans, pre-positioned containment gear, and clear spill mitigation procedures, particularly in these high-risk zones.

Ship-to-ship (STS) bunkering can be misused to mask unlawful activities such as sanctions evasion. According to the U.S. Office of Foreign Assets Control (OFAC), these transfers are among several deceptive shipping practices (DSPs) used to conceal the movement of fuel involved in sanctions evasion. Since STS bunkering takes place offshore, it complicates efforts to trace the fuel’s true source and destination, making monitoring and enforcement significantly more challenging.

Implications for Management

To support you in mitigating deceptive bunkering fuel transfers, Pole Star Global’s cutting-edge maritime intelligence solutions provide the transparency you need to identify this illicit activity by enabling you to:

• Track Vessel Behaviour in Real Time: Use Pole Star Global’s AIS and persistent tracking technology, combined with AI and human oversight, to monitor and analyse vessel movements. Key red flags include AIS signal loss, sudden course changes, or extended loitering in high-risk zones.
• Screen for Sanctions Compliance Instantly: As global sanctions regimes become increasingly complex, staying compliant is critical. With Pole Star Global’s PurpleTRAC platform, you can screen vessels, owners, operators, and cargoes in real time against major global sanctions lists, including OFAC. This empowers you to make informed decisions before bunkering or chartering.
• Set Custom Geofences & Receive Real-Time Risk Alerts: Define geofences around STS hotspots or restricted areas and receive automatic alerts the moment a vessel enters. This enables you to respond quickly when suspicious behaviour arises – no delays, no blind spots.
• Analyse Past Voyages for Hidden Patterns: Access detailed historical voyage data to uncover red flags, such as repeated unreported STS events, visits to sanctioned ports, or routes through known smuggling corridors.
• Embed Due Diligence into Chartering & Bunkering: Integrate Pole Star Global into your pre-fixture workflows to thoroughly vet vessels. By reviewing a vessel’s compliance and behavioural history, you can avoid working with high-risk operators and protect your operations from exposure.

Bunkering has long been a prime target for fraud.

Common schemes that exploit vulnerabilities in the bunkering process include:

• Fuel suppliers overcharging buyers by delivering less fuel than what has been paid for.
• Heating or aerating fuel to decrease its density while increasing its volume.
• Fuel suppliers conspiring with vessel officers to defraud the fuel purchaser.
• Vessels and fuel suppliers meeting outside established bunkering zones to buy smuggled or stolen fuel at a discount.
• Misrepresenting the type or quality of fuel to exploit pricing discrepancies.
• Forging delivery documentation related to fuel quantity, quality, or origin.
• Adulterating fuel by mixing different grades, adding cheaper substances, or combining it with water or other chemicals, then selling this lower-grade fuel at full price.

Analyses show that 39% of bunker fuel exhibits statistically significant discrepancies compared to its delivery paperwork. These fraudulent practices have knock-on effects throughout every part of the fuel supply chain. In total, they are estimated to add $5 billion to global shipping costs annually.

The widespread adoption of Very Low Sulphur Fuel Oils (VLSFO) as a bunker fuel has exacerbated the problem. VLSFO was developed to comply with new maritime fuel standards, but due to its diverse composition and largely untested environmental impact, it has been dubbed “Frankenstein fuel”. These fuels are difficult to detect because the standards for their chemical composition are so broad.

Fuel contamination is one of the most significant risks in bunkering.

This occurs when fuel is mixed with impurities or incompatible substances, potentially causing severe damage to a ship’s engines. The consequences include costly repairs, breakdowns, and serious safety hazards. In fact, in 2022 alone, poor-quality fuel and bunkering fraud cost shipowners an estimated £5 billion, leaving over 600 ships out of service.

The common ways bunkering fuel becomes contaminated are highlighted below:

• Contaminated Supply Source: The fuel is already contaminated before it reaches the ship. Common contaminants include water, sediments, chemical waste or cutter stocks, and microbial growth.
• Dirty Bunker Barges or Tanks: If the barge or tank used for transporting or storing fuel is not cleaned properly between different types of fuel or cargo, cross-contamination can occur. Residues from previous cargoes (e.g. waste oil or chemicals) can mix with fresh fuel.
• Water Ingress: Water can enter tanks through leaky hatches, faulty seals, condensation inside the tank, faulty hoses or connections during transfers, or ballast water contamination if tank segregation is inadequate.
• Mixing Incompatible Fuels: Blending incompatible fuels (e.g. residual fuels with distillates or unknown cutters) can lead to:
• Fuel instability,
• Sludge formation,
• Filter blockages and engine failure,
• Poor Bunkering Practices: Human error or poor procedures during bunkering can introduce contaminants. Risky practices to be aware of include:
• Not following pre-bunkering checklists,
• Not conducting proper sampling,
• Failing to flush lines or clean filters beforehand,
• Bunkering at too high a rate, causing agitation or mixing of sediments.
• Contaminated Shore Facilities: Onshore tanks and pipelines can accumulate residues, rust, or sludge over time. If not cleaned or maintained, these contaminants can be dislodged and transferred during bunkering.
• Microbial Contamination: Bacteria and fungi can grow in fuel tanks, especially at the water–fuel interface, producing sludge and acids that damage engines.

Fuel quality disputes are generally more difficult to resolve than quantity-related issues, as the root causes are not always immediately clear. In such cases, robust contractual protections and strict operational diligence are essential for mitigating risks.

Disputes over fuel quality are complicated by insufficient evidence, such as missing samples or incomplete fuel analysis reports. For instance, although ISO 8217:2024 sets out baseline fuel standards, there are cases where fuels meet these requirements and still contain unexpected substances that only become apparent through further testing. This makes it difficult to directly link fuel quality to engine damage. The situation has become even more complicated with the global shift towards low-sulphur fuels – often referred to as “Frankenstein fuels”. This transition has led to a wider variety of fuel blends, increasing the risk of inconsistency and contamination.

Best Practices for Mitigating Fuel Contamination Risk During Bunkering Operations

• Adhere to the Safety Management System (SMS): Ensure the vessel strictly follows the owner’s SMS procedures during bunkering. Conduct a thorough risk assessment beforehand to identify and mitigate potential hazards.
• Follow a Well-Defined Bunker Plan: Develop a comprehensive plan that clearly outlines the sequence of tank filling, the status of overflow tanks, and specific measures to prevent cross-contamination between different fuel types.
• Conduct an Independent Bunker Survey: Appoint a qualified independent surveyor to inspect the fuel quality and quantity, oversee proper sampling, and ensure all samples are correctly labelled, sealed, and documented.
• Ensure Thorough Documentation: Record every key event throughout the bunkering process – including start and stop times, flow rates, and any delays or irregularities. This detailed log serves as vital evidence in case of disputes.
• Rigorous Tank Preparation and Monitoring: Before and during bunkering, carry out a detailed inspection of all nominated tanks. Make sure non-nominated tanks are properly isolated to prevent contamination.
• Managing Off-Spec Fuel: If the fuel is found to be off-spec, respond promptly and appropriately based on the circumstances. This may involve consulting with experts, arranging further laboratory tests, and notifying the flag state or class society, if required.

On 1 January 2020, the IMO enforced the IMO 2020 regulation under MARPOL Annex VI, which drastically limits the sulphur content in marine fuels. The aim is to reduce harmful emissions from ships, significantly improve air quality, and safeguard marine ecosystems worldwide.

Furthermore, the IMO has set strict net-zero goals for 2050.

Bunkering operations lie at the heart of this transformation and must adapt to support the widespread adoption of cleaner energy sources.

What Is Green Fuel Bunkering?

Green fuel bunkering involves supplying ships with alternative, low-emission fuels such as liquefied natural gas (LNG), biofuels, green hydrogen, methanol, and ammonia. These fuels produce significantly fewer pollutants and greenhouse gas emissions (GHGs) compared to traditional marine fuels. However, they present unique challenges in terms of storage, handling, and infrastructure.

Unlike conventional fuel – which often share standardised infrastructure – most green fuels require dedicated facilities due to their specific safety and technical requirements.

• Hydrogen: One of the cleanest fuel options, hydrogen produces only water vapour when burned. However, it is highly flammable, has a low energy density, and requires specialised systems for safe storage and handling both onboard and at ports.
• Methanol: A renewable liquid fuel that is compatible with certain existing engines. While it offers environmental benefits, it requires specialised storage systems and strict handling protocols to control volatile organic compound (VOC) emissions during bunkering.
• Ammonia: A carbon-free fuel with strong environmental potential. However, its toxicity and corrosiveness demand advanced safety measures for both shipboard use and shore-based operations.
• Liquefied Natural Gas (LNG): Currently the most widely used alternative bunker fuel, LNG significantly reduces sulphur emissions, particulates, and greenhouse gases compared to traditional fuels. It is considered a transitional solution as the industry moves towards fully renewable options.

Infrastructure and Industry Implications

Shifting to green fuels demands a complete overhaul of port and ship infrastructure. This includes dedicated storage tanks, specialised fuelling and bunkering systems, and safety protocols tailored to each alternative fuel. The implications for bunkering operations are highlighted for each green fuel type outlined above.

Hydrogen Bunkering

In 2025, successful bunkering of liquid hydrogen took place at the Port of Amsterdam. In response, the Netherlands issued the first licence for hydrogen bunkering in ports, enabling the refuelling of vessels with liquefied hydrogen. While this milestone relied on truck-to-ship transfer, it shows potential to scale operations to achieve ship-to-ship bunkering.

The process of bunkering requires specialised equipment due to hydrogen’s unique properties, as previously mentioned. The equipment used is tailored to the type of hydrogen, compressed gas or liquid. Key components include hydrogen storage tanks, high-pressure or cryogenic transfer hoses, bunkering skids with flow control systems, and safety features such as leak detectors, inert gas purging, and emergency shutdown systems. Additional equipment, such as cooling units (for liquid hydrogen), grounding systems, and communication interfaces, ensures safe and efficient operations.

Methanol Bunkering

There have been several notable firsts in methanol bunkering, including truck-to-ship in 2015, shore-to-ship in 2016, and barge-to-ship in 2021, all of which have been successful. A considerable portion of the current infrastructure designed for marine gas oil and heavy fuel oil can be adapted to accommodate methanol bunkering needs, offering a five- to six-year head start over alternative marine fuels such as ammonia, liquefied biogas, electricity, and hydrogen.

However, the space required for storage and fuel tanks on methanol-powered ships is approximately 2.4 times greater than that on vessels using marine gas oil. This drawback can be mitigated by regular bunkering and the flexibility of methanol storage – methanol can be stored in standard fuel storage tanks and even in a vessel’s ballast tanks.

The Maritime and Port Authority of Singapore (MPA) is keen to develop a methanol bunkering hub. According to the MPA, the proposals received for low-carbon methanol supply and delivery are promising, with several projects already operational or having reached the Final Investment Decision (FID) stage. Collectively, these projects have the potential to supply over one million tonnes per year of low-carbon methanol by 2030, subject to commercial decisions and global developments.

Methanol bunkering requires equipment specifically designed to handle its unique properties, as detailed above. This includes stainless steel or coated storage tanks, explosion-proof pumps, and methanol-compatible hoses or loading arms with dry disconnects to prevent leaks. Vapour recovery systems, inert gas purging (typically using nitrogen), and flame arrestors are essential for managing methanol’s flammable vapours. Safety measures such as gas detection, emergency shutdown systems (ESD), grounding, and fire-fighting equipment must be in place, along with spill response kits and appropriate personal protective equipment (PPE). All systems must comply with IMO and class society standards to ensure safe and efficient operations.

Ammonia Bunkering

There have been several pilot projects and trials that have demonstrated the feasibility of transferring ammonia between vessels when at anchorage and berth. For instance, the Global Centre for Maritime Decarbonisation (GCMD) conducted a pilot transfer of 2,700 tonnes of ammonia between two gas carriers at the Port of Dampier, Western Australia, in September 2024. lus, the Port of Rotterdam completed its first ammonia bunkering pilot with a transfer between the Oceanic Moon and the Gas Utopia while at berth.

JERA and NYK Line conducted the first truck-to-ship bunkering operation for an ammonia-fuelled tugboat in Yokohama, Japan. Other notable trials include Trafigura’s successful ship-to-ship transfer of ammonia in international waters near the Port of Ceuta.

Ammonia bunkering requires specialised equipment due to its toxic and corrosive nature. Key components include ammonia-compatible storage tanks, double-walled transfer hoses or loading arms with dry-break couplings, and vapour return and inert gas systems for pressure control and safety. Comprehensive gas detection, emergency shutdown systems, and fire and spill response equipment are essential, along with full personal protective equipment (PPE) for all personnel. All systems must comply with international safety and classification standards to ensure safe operations.

LNG Bunkering

LNG bunkering has been established at various ports and regions around the world. The first ship-to-ship LNG bunkering took place at the Port of Stockholm, Sweden, in January 2013.

Currently, over 2% of the global shipping fleet is LNG-powered, with LNG gaining momentum due to its competitive pricing, abundant supply, and lower emissions. For instance, global LNG bunkering increased by 62% in 2023 compared to 2022.

LNG bunkering vessels are equipped with advanced systems to handle the extremely low temperature of the fuel and to ensure safety. Transport tanks are constructed with internal and external compartments and a vacuum system between them to minimise heat transfer. LNG bunkering requires insulated storage tanks, cryogenic transfer hoses or loading arms, vapour return lines, and emergency shutdown systems. Cryogenic pumps and flow metres ensure safe and accurate transfer, while gas detection and fire suppression systems help manage associated risks. Appropriate personal protective equipment (PPE) and clear ship-to-shore communication are also essential for safety and compliance.

As regulatory pressures and environmental expectations grow, investing in green bunkering capabilities is no longer optional. It is a crucial step for the long-term sustainability and competitiveness of the maritime sector.