Maritime sector leans towards dual pathway for zero-carbon fuels: green methanol and ammonia

The maritime sector’s search for a practical zero-carbon fuel has settled, for now, on two front-runners: green methanol and green ammonia. Both are being positioned as serious options for deep decarbonisation, yet they solve different engineering problems and create different operational risks. For shipowners, designers and fuel-system specialists, the choice is no longer theoretical. It is increasingly about which molecule best fits a vessel’s trading pattern, safety case, port access and retrofit economics.

Methanol has the easier physical profile. Because it remains liquid at ambient temperature, it can be stored and handled using infrastructure that is less demanding than the cryogenic or pressurised systems associated with some other alternative fuels. Rolls-Royce has pointed to that simplicity, alongside methanol’s relatively attractive production economics, as a reason it is developing methanol-capable marine engines. Industry groups such as Proman and Methanex also stress its availability, existing port access and strong reductions in sulphur oxides, particulate matter and nitrogen oxides compared with conventional bunker fuels.

That practicality, however, comes with a caveat. Methanol is only truly low-carbon if the carbon in it is sourced sustainably, typically through captured CO2 combined with renewable hydrogen. Without that upstream decarbonisation, it becomes a lower-emission transition fuel rather than a genuinely green one. A recent review in Renewable Energy noted that the combustion behaviour of methanol is manageable, but reliability issues such as lubrication failure and corrosion still need careful engineering attention.

Ammonia sits at the other end of the trade-off. Its principal attraction is that, when used as a fuel, it contains no carbon and therefore produces no CO2 at the point of combustion. That makes it especially appealing for ship operators aiming at the strictest long-term decarbonisation targets. Lloyd’s Register has described ammonia as one of the most promising low-carbon marine fuels, but it also underlined the major obstacles: toxicity, specialised handling requirements and the need for new port and vessel infrastructure. A review in Energy Reports found that ammonia could help shipping meet CO2 and NOx targets and may become more cost-competitive by 2050, but only if the sector overcomes the present safety and materials challenges.

Those challenges are not trivial. Ammonia demands rigorous containment, ventilation and emergency-response systems, as well as careful selection of materials that can tolerate its chemical behaviour. For crews and port workers, the hazards are materially different from those associated with methanol. That makes ammonia a stronger candidate for large-scale, highly controlled operations than for fleets seeking the simplest possible transition path.

The strategic question, then, is less about which fuel is universally superior and more about which is operationally viable in a given setting. Methanol has the advantage where fast adoption, bunkering familiarity and lower retrofit friction matter most. Ammonia may ultimately be better suited to longer-term deep decarbonisation, particularly on routes where the additional safety and infrastructure burden can be justified. In practice, vessel class, voyage length, engine choice and regional renewable-fuel supply will all shape the answer.

For marine decarbonisation, that means the market is unlikely to converge on a single winner. Instead, shipping may develop along two parallel tracks: methanol as the earlier, more manageable option, and ammonia as the harder but potentially cleaner end-state. For engineering teams, the task is to design systems flexible enough to support that transition without locking fleets into assumptions that may prove too narrow for the IMO’s 2050 ambitions.