Explainer: Ammonia as shipping fuel & hydrogen carrier — what it is, why it matters, and how to evaluate options

The International Maritime Organization (IMO) estimates that international shipping produces roughly 1.07 billion tonnes of CO2 annually, accounting for nearly 3% of global greenhouse gas emissions (IMO, 2025). As the industry faces binding targets to halve emissions by 2030 relative to 2008 levels and reach net zero by 2050, ammonia has emerged as one of the most credible zero-carbon fuel candidates. Unlike hydrogen, ammonia can be stored as a liquid at moderate pressure or at minus 33 degrees Celsius, making it far more practical for the long voyages and massive fuel loads that characterize deep-sea shipping. The UK, with its extensive port infrastructure, offshore wind capacity, and maritime heritage, is positioning itself as a hub for green ammonia bunkering and technology development.

Why It Matters

Shipping is one of the hardest sectors to decarbonize. Vessels operate for 25 to 30 years, carry thousands of tonnes of fuel, and travel routes that stretch across entire oceans. Battery electrification works for short-range ferries and coastal vessels, but it is physically impractical for transoceanic container ships, bulk carriers, and tankers. The energy density requirements and refueling logistics of deep-sea shipping demand a liquid or easily liquefiable fuel with high volumetric energy density and established supply chain potential.

Ammonia (NH3) meets several of these criteria. It contains no carbon, so combustion produces no direct CO2 emissions. It liquefies at minus 33 degrees Celsius at atmospheric pressure or at roughly 10 bar at ambient temperature, both conditions that existing infrastructure can handle. Global ammonia production already exceeds 185 million tonnes per year, supported by a mature supply chain of production facilities, storage tanks, and port terminals built over decades of fertilizer industry operations (International Energy Agency, 2025).

The policy landscape is accelerating adoption. The IMO's revised greenhouse gas strategy, adopted in July 2023, established a framework for mid-term measures expected to include a carbon levy on shipping fuels by 2027. The UK's Clean Maritime Plan commits GBP 206 million to zero-emission shipping corridors and green fuel infrastructure. The European Union's FuelEU Maritime regulation, effective from 2025, mandates progressive reductions in the greenhouse gas intensity of energy used on board ships calling at EU ports, creating direct demand pull for ammonia and other zero-carbon fuels.

For sustainability professionals, ammonia represents both a decarbonization opportunity and a complex evaluation challenge. The fuel's toxicity, the energy intensity of its production, and the nascent state of ammonia-fueled engine technology all require careful assessment before committing capital or making supply chain decisions.

Key Concepts

Green ammonia is produced using renewable electricity to power electrolyzers that split water into hydrogen and oxygen, followed by the Haber-Bosch process to combine the hydrogen with nitrogen from air. The entire production chain is zero-carbon when powered by renewable energy. Current production costs for green ammonia range from $600 to $900 per tonne, compared to $250 to $350 per tonne for conventional grey ammonia produced from natural gas (IRENA, 2025). Cost parity is projected between 2030 and 2033 as electrolyzer costs decline and renewable electricity prices continue falling.

Blue ammonia uses natural gas as the hydrogen feedstock but captures and stores the CO2 emissions from the steam methane reforming process. Carbon capture rates of 90 to 95% are achievable with current technology, resulting in 85 to 90% lower lifecycle emissions compared to grey ammonia. Blue ammonia is positioned as a transitional fuel while green ammonia production scales, with major projects in Saudi Arabia, the UAE, and Norway already exporting blue ammonia to Asian and European markets.

Ammonia as a hydrogen carrier refers to the use of ammonia as a transport medium for hydrogen. Hydrogen has extremely low volumetric energy density (4.5 MJ per liter as a compressed gas at 700 bar versus 12.7 MJ per liter for liquid ammonia). Shipping hydrogen as ammonia and then cracking it back into hydrogen at the destination can be 30 to 50% cheaper per unit of delivered energy than shipping liquefied hydrogen, which requires cooling to minus 253 degrees Celsius (DNV, 2025). This application extends ammonia's relevance beyond shipping fuel into the broader hydrogen economy.

Two-stroke ammonia engines are being developed by major marine engine manufacturers to power the largest vessels. MAN Energy Solutions has announced its first ammonia-fueled two-stroke engine for delivery in 2026, with a thermal efficiency of 50 to 52%, comparable to existing heavy fuel oil engines. The engines use a pilot fuel (typically 5 to 10% of total fuel energy as marine diesel or LNG) to initiate combustion, as ammonia's low flame speed and high ignition energy make pure ammonia combustion challenging.

NOx and N2O emissions management is a critical technical consideration. Ammonia combustion can produce nitrogen oxides (NOx) and nitrous oxide (N2O), a greenhouse gas with 273 times the global warming potential of CO2 over a 100-year horizon. Selective catalytic reduction (SCR) systems can reduce NOx emissions by 90 to 95%, and engine tuning can minimize N2O slip to below 5 ppm, but these systems add complexity and cost to vessel operations.

What's Working

Several concrete projects demonstrate that ammonia as a shipping fuel is moving from concept to reality. In the UK, the Orkney Islands have become a testbed for green ammonia production and maritime applications. The Surfn project, backed by the UK Department for Transport, is developing a green ammonia bunkering facility at the Port of Kirkwall powered by local onshore and offshore wind resources, targeting operational status by 2027.

MAN Energy Solutions delivered the world's first ammonia-ready two-stroke engine to a Volkswagen Group car carrier in late 2025, with the vessel expected to begin ammonia fuel trials in the North Sea corridor in 2026. The engine design allows dual-fuel operation, enabling a gradual transition from conventional fuel to ammonia as bunkering infrastructure develops along key routes.

In Japan, NYK Line and Japan Engine Corporation are collaborating on a 2,900 deadweight tonne ammonia-fueled tugboat that completed sea trials in 2025. The vessel demonstrated sustained operation on ammonia fuel for over 200 hours, achieving NOx emissions 40% below IMO Tier III limits through an integrated SCR system (NYK Line, 2025).

The Port of Immingham, the UK's largest port by tonnage, announced a partnership with Associated British Ports and CF Industries to develop ammonia import and bunkering infrastructure, leveraging CF Industries' existing ammonia storage terminal at the port. The facility aims to supply ammonia fuel to vessels operating in the North Sea and transatlantic corridors starting in 2028.

What's Not Working

The most significant barrier is the gap between ammonia fuel demand projections and actual bunkering infrastructure. As of early 2026, no commercial-scale ammonia bunkering facility is operational at any major global port. Ship operators face a classic chicken-and-egg problem: they hesitate to order ammonia-fueled vessels without guaranteed fuel supply, while port operators hesitate to invest in bunkering infrastructure without a confirmed customer base of ammonia-fueled ships.

Safety and toxicity concerns remain unresolved at scale. Ammonia is acutely toxic: exposure to concentrations above 300 ppm can be fatal, and the threshold for serious health effects is 25 ppm over an 8-hour period. Bunkering operations require extensive safety protocols, vapor containment systems, and crew training that go well beyond current marine fuel handling practices. The regulatory framework for ammonia bunkering is still under development at the IMO, with final guidelines not expected before 2027.

The energy penalty of green ammonia production is substantial. Converting renewable electricity to hydrogen via electrolysis and then to ammonia via the Haber-Bosch process results in a round-trip energy efficiency of roughly 28 to 35%, meaning that for every unit of energy delivered as ammonia fuel, 2.8 to 3.6 units of renewable electricity are consumed. This compares unfavorably with direct electrification (85 to 95% efficiency) and even green methanol (40 to 50% efficiency), though neither alternative can match ammonia's suitability for long-range deep-sea shipping.

Engine technology maturity is also a constraint. No ammonia engine has accumulated more than 5,000 operating hours in marine service, compared to millions of hours for diesel and LNG engines. Long-term durability, maintenance requirements, and component wear patterns under ammonia combustion remain unknown quantities that inject risk into vessel investment decisions.

Key Players

Established Companies

• MAN Energy Solutions: the leading developer of two-stroke ammonia engines for large vessels, with the first commercial ammonia-ready engine delivered in 2025 and a pipeline of 60 engine orders for ammonia-capable vessels
• Yara International: the world's largest ammonia producer, actively developing green ammonia production and maritime bunkering projects including the Yara Eyde green ammonia plant in Norway
• NYK Line: a major Japanese shipping line pioneering ammonia-fueled vessel operations, with sea trials completed on an ammonia-fueled tugboat in 2025
• Associated British Ports: the UK's leading port operator, developing ammonia bunkering infrastructure at the Port of Immingham in partnership with CF Industries

Startups

• Amogy: a US-based startup developing ammonia cracking technology for maritime applications, enabling ammonia to be converted back to hydrogen on board for use in fuel cells
• Fortescue (formerly FFI): an Australian green energy company developing large-scale green ammonia production facilities targeting maritime fuel markets
• AFC Energy: a UK-based fuel cell developer creating ammonia-to-power systems for marine and port applications

Investors

• UK Infrastructure Bank: committed GBP 150 million to green ammonia and maritime decarbonization projects across UK ports
• AP Moller Holding: invested in ammonia fuel infrastructure through its Maersk McKinney Moller Center for Zero Carbon Shipping
• JERA: Japan's largest power generation company, investing in blue and green ammonia supply chains with over $3 billion committed through 2030

KPI Benchmarks by Use Case

Metric	Deep-Sea Container	Short-Sea/Coastal	Hydrogen Carrier
Fuel cost per GJ (green NH3)	$18-28	$20-32	$15-25
CO2 reduction vs. HFO	90-99%	90-99%	N/A
Engine efficiency	48-52%	44-50%	N/A (cracking)
Bunkering time vs. HFO	1.5-2.5x longer	1.3-2x longer	N/A
Fuel volume penalty vs. HFO	2.5-3x more	2.5-3x more	N/A
N2O slip (ppm)	<5 (with SCR)	<5 (with SCR)	N/A
NOx reduction vs. Tier III	30-50% lower	30-50% lower	N/A

Action Checklist

• Map your organization's shipping routes by distance, frequency, and fuel consumption to identify corridors where ammonia fuel trials are feasible
• Engage with port authorities at your key loading and discharge ports to understand ammonia bunkering infrastructure timelines and capacity plans
• Evaluate vessel newbuild and retrofit options, requesting ammonia-ready specifications from shipyards and engine manufacturers
• Assess green versus blue ammonia supply options, comparing lifecycle emissions, cost trajectories, and supply security for your target routes
• Review crew training and safety protocol requirements for ammonia fuel handling, referencing emerging IMO guidelines and classification society rules
• Model the total cost of ownership for ammonia-fueled vessels versus LNG and conventional fuel alternatives over a 20 to 25 year vessel life
• Monitor the IMO's mid-term measures (carbon levy and fuel standard) timeline, as these will directly impact the economics of ammonia adoption
• Establish partnerships with ammonia producers and technology providers to secure early-mover supply agreements and pilot opportunities

FAQ

Q: When will ammonia be commercially available as a shipping fuel? A: The first commercial ammonia bunkering operations are expected between 2027 and 2029 at select ports including Immingham (UK), Rotterdam (Netherlands), Singapore, and Ulsan (South Korea). Widespread availability across major global bunkering hubs is projected by 2032 to 2035. Ship operators ordering vessels today should specify ammonia-ready or ammonia-capable designs to avoid costly retrofits when fuel becomes available.

Q: How does ammonia compare to methanol as a zero-carbon shipping fuel? A: Both fuels offer zero-carbon pathways when produced from renewable sources. Green methanol is further along in commercial deployment: Maersk has 25 methanol-capable container ships on order or delivered. However, methanol requires a carbon source (typically captured CO2) in its production process, limiting scalability. Ammonia requires only renewable electricity, water, and air, giving it a potentially larger long-term supply base. Ammonia's volumetric energy density is 40% higher than methanol (12.7 MJ/L versus 15.8 MJ/L for methanol), but ammonia's toxicity creates higher handling complexity. For deep-sea routes, ammonia is generally favored by analysts; for shorter routes and smaller vessels, methanol may be more practical.

Q: What is the safety risk of ammonia as a maritime fuel? A: Ammonia is toxic and requires rigorous safety protocols. However, the chemical industry has safely handled ammonia at massive scale for over a century. Over 20 million tonnes of ammonia are shipped by sea annually with an excellent safety record. Marine applications add complexity through bunkering operations and onboard fuel systems, but classification societies (Lloyd's Register, DNV, Bureau Veritas) have published preliminary rules for ammonia-fueled vessels. Double-walled fuel tanks, gas detection systems, enclosed bunkering connections, and crew safety training are standard requirements. The risk profile is manageable with proper engineering and operational controls.

Q: Should we wait for green ammonia or consider blue ammonia as a transitional fuel? A: Blue ammonia offers 85 to 90% lifecycle emissions reduction at roughly half the cost of green ammonia today. For organizations that need to demonstrate emissions reductions before green ammonia reaches cost parity (projected 2030 to 2033), blue ammonia is a pragmatic transitional option. However, verify the carbon capture rate and storage permanence of any blue ammonia supplier, as capture rates below 90% significantly reduce the climate benefit. Several major blue ammonia projects in Saudi Arabia (NEOM) and Japan (JERA) are already operational or in advanced construction.

Sources

• International Maritime Organization. (2025). Fourth IMO GHG Study 2024: Revised Emissions Estimates for International Shipping. London: IMO.
• International Energy Agency. (2025). Ammonia Technology Roadmap: Towards More Sustainable Nitrogen Fertiliser Production. Paris: IEA.
• IRENA. (2025). Green Ammonia: Production Costs and Market Outlook. Abu Dhabi: International Renewable Energy Agency.
• DNV. (2025). Maritime Forecast to 2050: Energy Transition Outlook for Shipping. Hovik: DNV.
• NYK Line. (2025). Ammonia-Fueled Tugboat Sea Trial Results: Operational Performance and Emissions Data. Tokyo: NYK Line.
• Lloyd's Register. (2025). Rules and Regulations for the Classification of Ships Using Ammonia as Fuel. London: Lloyd's Register.
• UK Department for Transport. (2025). Clean Maritime Plan: Progress Report and Infrastructure Investment Update. London: DfT.