The shipping industry is responsible for between 2 and 3% of all global emissions. In recognition of this, the International Maritime Organization has set the ambitious goal to fully decarbonise the sector by 2050. Hitting this target will require a wide-scale transition from today’s high-emission fossil fuels to zero-emission alternatives.
While the Global Maritime Forum is fuel agnostic and does not endorse the use of one type of alternative fuel over another, methanol and ammonia have emerged as two of the most promising candidates among the options under consideration. Each has its own distinct advantages, challenges, and pathways to scale.
This Q&A explains how ammonia and methanol work, how they compare, and where they fit alongside other emerging fuel options.
Why are methanol and ammonia being used as shipping fuels?
Methanol and ammonia are considered two of the most promising alternative shipping fuels due to their potential to significantly reduce ships’ emissions, decrease in cost over time, and achieve the scale of production needed to decarbonise the sector (replacing around 300 million tonnes of fuel oil per year).
How much can ammonia and methanol reduce shipping emissions?
Both ammonia and methanol can be low- or zero-emission fuels.
A key attraction of ammonia as a shipping fuel is that it does not contain carbon and thus does not produce carbon emissions when burnt. Advanced engine testing results suggest that 90-95% reductions in tank-to-wake emissions (i.e., the emissions resulting from direct fuel combustion onboard the vessel) are plausible with the engines under development.
Methanol contains carbon, but if it is made from renewable sources (so-called green methanol, see more below), it can still be a net-zero emission fuel even though it emits CO2.
What other emissions are produced when using ammonia and methanol as shipping fuels?
While ammonia can greatly reduce carbon emissions, its use as a shipping fuel presents other emissions risks:
• Ammonia slip - highly toxic, presenting a safety risk to people and the environment
• Nitrogen oxides (NOx) - contribute to the formation of acid rain and smog
• Nitrous oxide (N₂O) - a greenhouse gas 273 times stronger than carbon dioxide over a 100-year timeframe
• Greenhouse gases from the pilot fuel required for engine ignition
Recent research studies and NGO advocacy have suggested that these emissions could be a major stumbling block for ammonia if they are not adequately addressed.
The use of methanol can also produce nitrogen oxides and greenhouse gases from pilot fuel, but it does not pose the risk of slip or nitrous oxide emissions.
What is the current status of methanol and ammonia as shipping fuels?
Shipping’s transition to zero-emission fuels and technologies is expected to follow an S-curve, in which an initial period of slow uptake (emergence) is followed by a rapid increase (diffusion), before eventually flattening out (reconfiguration).
Both methanol and ammonia are still in the emergence phase. This phase can be further broken down into three sub-stages:
Proof of concept, reached once a fuel has been shown to be safe and effective in real-world demonstrations
Initial scale, reflecting small-scale commercial adoption of the fuel on specific routes and ports
Maturity, marking the fuel’s development into a widely available solution, with limited barriers to uptake.
How far are ammonia and methanol in their development as shipping fuels?
Methanol is moving towards initial scale, with around 60 methanol-capable vessels on the water, more than 300 further ships on order, and just under 20 ports offering green methanol bunkering.
Meanwhile, ammonia is rapidly approaching proof of concept as a shipping fuel, with the first ammonia-powered vessels successfully piloted, engine testing near completion, and bunkering trials underway at major ports.
When will methanol and ammonia be in widespread use as shipping fuels?
This is perhaps the biggest question. If the shipping industry is to meet its decarbonisation goals, zero-emission fuels, such as green methanol and ammonia, need to rapidly scale from around 2030. While both ammonia and methanol are expected to see uptake in the sector by 2030, it is a matter of how much. Currently, the biggest challenge to scaling the fuels is the supply chain. For methanol, the availability of green molecules (see below) is the biggest hurdle, while for ammonia, it is a lack of commercial ammonia bunkering at key ports.
How much ammonia or methanol is needed to power a ship?
This would depend on several factors, but both ammonia and methanol have lower energy densities than traditional fuels.
This means that ships will need larger tanks than those currently used for conventional fuels and/or will need to refuel more often. Early experiences with methanol-powered vessels have shown that the fuel’s lower energy density is not an insurmountable problem but creates a trade-off because these vessels need to bunker twice as frequently as they usually would.
Ammonia is even less energy-dense than methanol, so ships running on ammonia would need even larger storage solutions or would have to refuel more than twice as often as conventional ships.
Are methanol and ammonia dangerous to use as shipping fuels?
Each fuel presents its own handling challenges and associated safety risks, just like traditional fuels.
Ammonia is a highly toxic gas. While its strong smell makes leaks easy to detect, it can cause serious harm to people and the environment if released. It must be stored as a liquid either in pressurised tanks or at very cold temperatures, and requires the use of protective equipment and significant changes to ship design.
Methanol is a liquid fuel that does not require cooling or pressurisation, making it easier to store and transport, and allowing the use of existing infrastructure with limited modifications. It can be harmful in high concentrations or if it touches the skin. But the greater risk concerns fires. Methanol is highly flammable, and it is difficult to see a methanol flame in daylight. However, these challenges are manageable and smaller than those associated with ammonia.
The safety challenges of both fuels have been a major focus of the shipping industry. Many studies and initial pilots have been undertaken to test and validate the best way to handle the fuels, and training programmes for crew members are also underway. These efforts have not revealed any safety-related showstoppers for either fuel so far.
What are green, blue and grey methanol and ammonia shipping fuels?
Both ammonia and methanol are often referred to with a colour that describes the way they are made.
Green ammonia, also called e-ammonia, is produced using hydrogen made from renewable electricity-powered electrolysis and nitrogen. Green methanol refers to both e-methanol, produced using hydrogen from renewables-based water electrolysis and sustainable carbon, and bio-methanol, produced using waste or residual biomass feedstocks. Depending on exactly how they are produced and used, both green ammonia and methanol can be near-zero emissions.
“Blue” variants of ammonia and methanol are produced from fossil fuels but utilise carbon capture and storage (CCS). Blue ammonia and blue methanol produce fewer emissions than conventional fuels but are not considered zero-emission alternatives.
There are also “grey” variants. Grey methanol and grey ammonia are produced with unabated natural gas and, like other fossil fuels, have a significant climate impact.
What are the main alternatives to methanol and ammonia as shipping fuels?
While methanol and ammonia are two of the most discussed options, other fuels are also being explored, including methane/liquified natural gas (LNG), biodiesel, hydrogen, and electricity for short-sea applications. Each has different strengths, weaknesses, and levels of readiness.
How does LNG compare to methanol and ammonia as a shipping fuel?
Liquefied natural gas is already being used as a shipping fuel, with a mature global bunkering network and many vessels in operation. As of 2024, roughly 7% of the global fleet could utilise LNG. While LNG produces lower CO₂ emissions than heavy fuel oil and significantly reduces air pollutants such as sulphur oxides, it is still a fossil fuel and emits carbon dioxide. Its use can also release methane, a potent greenhouse gas that is around 30 times stronger than carbon dioxide over a 100-year timeframe and more than 80 times stronger over a 20-year period. This presents a serious challenge to LNG’s emissions reduction potential.
How do biofuels compare to methanol and ammonia as shipping fuels?
Biofuels (such as biodiesel or bio-oil) can be sustainably produced from waste oils, crop residues, or purpose-grown biomass. They can often be used in existing ship engines with minimal modification, making them a relatively simple near-term option.
Despite their drop-in compatibility with current ships, biofuels are not expected to be as scalable as ammonia or methanol and its life cycle emissions can vary significantly depending on feedstock and production process. Biofuels also currently have a lower price point than green methanol and ammonia, but this is expected to change over time as a lack of supply drives up prices. In contrast, the costs of ammonia and, to a lesser extent, methanol are expected to fall as production scales up.
For these reasons, biofuels are not considered scalable zero-emission fuels (SZEF), as defined by the annual ‘Progress Towards Shipping’s 2030 Breakthrough’ report produced by the UCL Energy Institute, UN Climate Change High-Level Champions, and the Getting to Zero Coalition (a Global Maritime Forum initiative).
How does hydrogen compare to methanol and ammonia as a shipping fuel?
Hydrogen can be used directly in fuel cells or internal combustion engines, and if produced from renewable sources, it emits no greenhouse gases. However, it has an even lower energy density than both ammonia and methanol, meaning its greatest potential is on short-sea or domestic ships. Hydrogen must also be stored as a cryogenic liquid at around –253 °C or under high pressure, which makes handling and storage challenging on board ships. There is currently very limited bunkering infrastructure for hydrogen, putting its development as a shipping fuel far behind that of ammonia and methanol.
Can battery power compete with methanol and ammonia in shipping?
Batteries can be a zero-emission shipping solution and are already powering short-sea ferries and small vessels. They are highly energy-efficient but store far less energy per weight and volume than liquid fuels, making them currently unsuitable for long-distance shipping. There is limited recharging infrastructure and renewable electricity. As such, it is not currently considered a serious contender to methanol and ammonia on board large ships
So, are methanol and ammonia the best options for reducing shipping emissions?
There is no single fuel that will decarbonise shipping on its own. Methanol and ammonia show significant promise and are expected to play important roles, but they will share the stage with other alternatives such as bio- and e-methane, liquid biofuels, hydrogen, and battery-electric solutions in specific segments. Each option comes with trade-offs regarding emissions, cost, safety, and infrastructure needs, and the right choice will depend on factors like vessel type, route, and timeframe. What is clear is that rapid investment, coordinated regulation, and large-scale deployment of zero- and near-zero-emission fuels will be essential if the sector is to meet its 2050 decarbonisation target.
To learn more, read ‘From pilots to practice: Methanol and ammonia as shipping fuels’.