The shipping industry could gain another option in its transition to lower-emission operations, with new research identifying ethanol as a potential marine fuel for both methanol-capable vessels and certain conventional diesel-powered ships.

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A study by the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping examines the technical requirements, safety considerations and commercial prospects of adopting ethanol across the existing fleet. The report, Ethanol as a Marine Fuel: Exploring Its Usability, was developed with industry partners including NORDEN, TotalEnergies and ABS.

Ethanol could have an advantage over emerging marine fuels because production and distribution infrastructure already exists in major markets, including the United States and Brazil. Its potential use in existing engine technologies could also help shipowners explore alternative fuels without relying entirely on new vessel designs.

However, the research highlights significant differences between using ethanol in methanol-compatible engines and blending it with conventional marine diesel.

Methanol-Compatible Ships Offer a Near-Term Opportunity

Researchers found that ethanol could be used in engines designed for methanol with relatively limited modifications. Because the two fuels have similar chemical properties, adjustments to fuel injection timing and engine controls may be sufficient to support ethanol operation.

Ethanol also has a higher energy density than methanol, potentially allowing vessels to carry less fuel to achieve a comparable operating range.

The remaining work largely involves optimizing engine performance, validating the technology and securing the necessary certifications, according to the study.

Maersk has been exploring this option aboard its methanol-fueled container ship Laura Maersk since 2025. Testing began with a 10% ethanol blend before progressing to higher concentrations. In June 2026, the company reported successful trials using pure ethanol.

The company has also advanced toward commercial fuel supply. A recent bunkering operation in Houston involved the 9,016-TEU Tangier Maersk. Maersk described the operation as the first commercial ship-to-ship ethanol bunkering of a deep-sea container vessel in the United States.

Engine manufacturers are also investigating ethanol applications. Everllence, WinGD, Wärtsilä and HD Hyundai have reported progress in testing the fuel, while Caterpillar announced conversion kits in July for selected MaK engines designed to operate on methanol or ethanol.

Diesel-Ethanol Blends Face Safety and Stability Challenges

Expanding ethanol use to conventional diesel-powered ships could open a much larger market, but the technical challenges are more substantial.

The study evaluated mixtures of ethanol and marine gas oil, focusing on fuel stability, combustion characteristics and safety requirements. Researchers identified two major obstacles.

The first is flashpoint, a critical safety consideration for marine fuels. Even a small proportion of ethanol significantly reduced the flashpoint of the tested mixtures. A blend containing 10% ethanol recorded a flashpoint of approximately 13.5°C, well below the 60°C minimum generally required under SOLAS for conventional marine fuels.

Laboratory attempts to raise the flashpoint by adding biodiesel and another additive did not succeed.

Fuel stability presented a second problem. The tested ethanol-diesel mixtures separated during storage, particularly at lower temperatures. All three blends examined separated after one week at 10°C, raising concerns about reliable fuel storage and handling aboard vessels.

One potential solution is onboard blending, which would mix ethanol and diesel shortly before the fuel enters the engine rather than storing the combined mixture for extended periods.

However, this approach would not eliminate the need to address flashpoint risks. Vessels would still require appropriate safety measures and potentially modified fuel systems.

Retrofitting Could Cost Less Than a Full Methanol Conversion

Despite these challenges, the research suggests that ethanol blends could offer an economically attractive retrofit option for some existing ships.

Using a Kamsarmax bulk carrier as a case study, the researchers estimated that modifying a vessel to operate on ethanol-marine gas oil blends could cost about half as much as converting it to full methanol dual-fuel capability.

The economic assessment considered a 30% ethanol blend and compared operating costs with conventional marine fuels under emissions-pricing assumptions based on the draft IMO Net-Zero Framework.

Under the baseline scenario, the conversion was not cost-competitive with continued use of very low-sulfur fuel oil.

The outlook improved for vessels operating mainly in sulfur emission control areas, ships with higher annual fuel consumption and operators able to secure ethanol with a particularly low lifecycle carbon intensity.

The study also found that a large container ship consuming around 25,000 tonnes of fuel annually could make a 30% ethanol blend economically viable across a broader range of fuel carbon intensities.

These results remain dependent on fuel prices, future emissions regulations and the availability of ethanol produced with sufficiently low greenhouse gas emissions.

Sustainability Will Determine Ethanol’s Long-Term Role

The study does not establish how much ethanol could contribute to shipping’s overall decarbonization. Although global production is already substantial, the fuel’s environmental performance varies according to feedstocks, farming practices, land-use changes and production methods.

The Center plans to examine sustainability, lifecycle emissions and production scalability in separate reports.

That distinction matters for shipowners evaluating alternative fuels. Ethanol’s compatibility with marine engines does not automatically mean that every ethanol supply delivers meaningful emissions reductions.

For vessels already equipped with methanol-compatible engines, ethanol could provide another fuel option when availability, pricing and emissions performance make it attractive. This flexibility could reduce reliance on a single alternative-fuel pathway.

For the much larger conventional diesel fleet, adoption will depend on resolving fuel safety and stability concerns while demonstrating that retrofit costs can be justified.

The findings point to a possible expansion in ethanol’s role in maritime transport, but wider adoption will depend on further technical validation, regulatory acceptance and access to sustainable fuel supplies.