The candidates compared
The most important number in maritime decarbonisation is a pair: more than 50% of newbuilding tonnage on order is designed for alternative fuels, while over 90% of the active fleet by tonnage still runs on conventional fuel (UNCTAD, Review of Maritime Transport 2025).
The industry has committed on the order book and has barely started on the water. Everything about the transition follows from that gap.
| Fuel | Energy density | Emissions profile | Handling risk | Infrastructure | Crew competency demand |
|---|---|---|---|---|---|
| LNG | Moderate (cryogenic) | Lower CO₂, SOₓ, PM; methane slip is the issue | Cryogenic, flammable | Established and growing | High — IGF/IGC competencies |
| Methanol | Low (about half of fuel oil) | Lower SOₓ/PM; carbon benefit depends on production route | Toxic, low flashpoint, invisible flame | Growing | Moderate to high |
| Ammonia | Low | No carbon at point of use; N₂O and slip concerns | Highly toxic | Early | Very high |
| Biofuel (FAME/HVO) | Similar to fuel oil | Depends on feedstock and lifecycle | Familiar; stability and storage issues | Drop-in capable | Low |
| Hydrogen | Very low volumetric | No carbon at point of use | Extreme flammability, storage | Very early | Very high |
| Nuclear | Extremely high | No operational carbon | Regulatory and public acceptance | Negligible | Specialised |
Volumetric energy density is the constraint people underestimate. A fuel with half the energy per cubic metre needs twice the tank volume for the same range — volume that comes out of cargo capacity, or out of range.
Why methane slip changed the LNG conversation
LNG delivers real reductions in sulphur oxides, particulates and — depending on engine technology — carbon dioxide. But unburnt methane passing through the engine is a potent greenhouse gas, and two regulatory changes brought it into the money:
- EU ETS covers methane and nitrous oxide alongside CO₂ from 2026
- FuelEU Maritime calculates greenhouse gas intensity on a well-to-wake basis against the 91.16 gCO₂e/MJ baseline
An LNG vessel whose engines slip significantly now carries a measurable financial penalty for it. Engine technology varies substantially in this respect, and it has become a purchasing criterion rather than a technical footnote.
The production route decides everything
For methanol, ammonia and hydrogen, the emissions benefit depends entirely on how the fuel was made:
| Route | Carbon outcome |
|---|---|
| Fossil-derived, unabated | Little or no lifecycle benefit |
| Fossil-derived with carbon capture | Partial benefit |
| Biogenic feedstock | Substantial benefit, feedstock-dependent |
| Renewable electricity (e-fuels) | Largest benefit; currently the most expensive |
Well-to-wake accounting under FuelEU means the regulation itself distinguishes these. A vessel burning fossil-derived methanol does not achieve what a vessel burning e-methanol achieves, and the compliance calculation reflects that.
The competency gap
This is the constraint that will bind first, and it gets the least attention.
| Fuel | What crews must be trained for |
|---|---|
| LNG | Cryogenic handling, gas detection, bunkering procedures, IGF competencies |
| Methanol | Toxicity, low flashpoint, invisible flame firefighting, tank inerting |
| Ammonia | Extreme toxicity, leak detection, respiratory protection, medical response |
| Biofuel | Storage stability, microbial growth, filter and seal compatibility |
Against a workforce of 2.57 million seafarers, an officer shortfall of 39,100 and a requirement for 113,735 more by 2030, retraining the fleet's crews for new fuels is a decade-long programme that has to run alongside a recruitment programme that is already behind.
Owners ordering alternative-fuel tonnage should be budgeting for competency, not only for the ship. Ammonia in particular is not a fuel that tolerates a thin training programme — it is acutely toxic, and the operational and emergency response requirements are unlike anything most crews have handled.
What owners should do
- Preserve optionality at newbuilding. Fuel-flexible engines and tank space provision cost far less at build than as a retrofit.
- Model well-to-wake, not tank-to-wake. It is what FuelEU measures and what the IMO framework contemplates.
- Contract for fuel supply carefully. Specification, availability at your ports, and the certification of the production route.
- Invest in competency early. Simulator training and structured familiarisation, budgeted per officer.
- Do the operational work now. Hull management, speed and arrival planning reduce emissions and cost under every regime, immediately.
- Watch methane slip specifications on any LNG dual-fuel purchase.
- Keep watching the IMO. The Net-Zero Framework was approved in April 2025, its adoption adjourned in October 2025, with talks resuming late 2026 — and its final shape will influence relative fuel economics.
fleet fuel data from UNCTAD RMT 2025; workforce data from BIMCO/ICS 2026; regulatory references to Directive (EU) 2023/959 and Regulation (EU) 2023/1805. Energy density figures are approximate volumetric comparisons for illustration. Reviewed by the Zeaclub Editorial Team, 24 August 2026.
Frequently asked questions
Which alternative fuel will win?
Most likely none exclusively. Different segments and trades will land differently — LNG and methanol on deep-sea tonnage now, ammonia later where safety and supply mature, biofuel as a transitional drop-in, and battery-electric in short-sea and harbour operation.
Is LNG a genuine decarbonisation fuel?
It reduces sulphur oxides, particulates and typically carbon dioxide, but its lifecycle benefit depends heavily on methane slip, which is now priced under EU ETS and measured under FuelEU.
Why is ammonia difficult?
It is acutely toxic. Handling, leak detection, personal protection and emergency medical response requirements are far more demanding than for any conventional marine fuel.
What is the real bottleneck?
Not vessel technology — more than half of newbuild tonnage on order is already alternative-fuel capable. The bottlenecks are fuel production at scale, bunkering infrastructure, and trained crews.