Maersk has completed what it calls the first ship-to-ship commercial ethanol bunkering of a deep-sea container vessel in the United States, fueling the 9,016-TEU Tangier Maersk in Houston. The operation, disclosed alongside a new study from the Mærsk Mc-Kinney Møller Center for Zero Carbon Shipping, signals that ethanol has moved from technical curiosity to a serious candidate in shipping's fuel transition.

The report, Ethanol as a Marine Fuel: Exploring Its Usability, published Thursday, was conducted with partners including Danish operator NORDEN, TotalEnergies and classification society ABS. It examined two pathways: burning ethanol in engines designed for methanol, and blending ethanol with marine gas oil for the much larger fleet of conventional diesel-powered ships.

The timing matters for shipowners weighing orderbook decisions. Operators are looking beyond methanol and ammonia for fuels that can be produced and supplied at scale, and ethanol already benefits from established production and distribution networks in the United States and Brazil. Fuels requiring entirely new supply chains do not have that head start.

What works today?

For methanol-capable vessels, the answer is: quite a lot. Because ethanol and methanol share similar chemical properties, engines designed for methanol can generally run on ethanol after adjustments to fuel injection timing and engine controls. Ethanol also carries a higher energy density than methanol, meaning a ship needs less tank capacity to achieve the same range.

The remaining challenges are largely engine optimization, validation and certification rather than major technical barriers, according to the report.

Maersk has been testing the fuel aboard the methanol-fueled container vessel Laura Maersk since 2025, starting with a 10% ethanol blend before moving to higher concentrations. In June 2026, the company reported successful trials using 100% ethanol.

Engine manufacturers are moving in parallel. Everllence, WinGD, Wärtsilä and HD Hyundai have all reported progress testing ethanol in marine engines. Caterpillar went further in July, announcing conversion kits for certain MaK engines to operate on methanol or ethanol.

Why diesel blends are harder

The picture darkens for conventional diesel ships. Researchers tested ethanol-marine gas oil blends for fuel stability, combustion properties and safety, and found two significant problems.

• A blend containing just 10% ethanol had a measured flashpoint of approximately 13.5°C — well below the 60°C minimum generally required under SOLAS for conventional marine fuels. Attempts to lift the flashpoint using biodiesel and another additive failed in laboratory tests.
• All three blends tested separated after one week in storage at 10°C, raising concerns about fuel handling and reliability at sea.

Researchers identified onboard blending systems as one possible fix, mixing ethanol and diesel shortly before the fuel enters the engine rather than storing them together. Even so, the low flashpoint would still demand safety equipment and modifications to onboard fuel systems.

Does the economics stack up?

For some vessels, possibly. Using a Kamsarmax bulk carrier as a case study, researchers estimated that modifying the ship for ethanol-marine gas oil blends would cost approximately half as much as a full conversion to methanol dual-fuel capability.

The analysis assumed a 30% ethanol blend and compared operating costs against conventional marine fuels under emissions pricing based on the draft IMO Net-Zero Framework. Under baseline assumptions, the conversion was not competitive with simply continuing on very low-sulfur fuel oil.

The economics improved considerably, however, for ships operating primarily in sulfur emission control areas, for vessels with higher annual fuel consumption, and for operators able to source ethanol with particularly low lifecycle carbon intensity. A large container ship consuming roughly 25,000 tonnes of fuel annually, for example, could economically run on a 30% ethanol blend across a wider range of fuel carbon intensities.

Those conclusions hinge on the future regulatory framework, fuel prices and the availability of ethanol produced with sufficiently low greenhouse gas emissions.

What ethanol does not yet answer

The report stops short of estimating how much ethanol could realistically contribute to shipping's overall decarbonization. Ethanol's environmental performance varies considerably depending on feedstocks, agricultural practices, land-use changes and production methods. The Center said sustainability, lifecycle emissions and scalability will be addressed in separate reports.

That distinction matters. Technical suitability does not make every source of ethanol a low-emission marine fuel.

For shipowners, the immediate gain is fuel flexibility: methanol-capable vessels could switch to ethanol when supplies or prices make it attractive, reducing dependence on any single alternative-fuel pathway. For conventional diesel tonnage, the opportunity remains more complicated, requiring additional investment and solutions to the stability and safety problems the study documented.

As the IMO's net-zero framework moves toward finalization, the spread between compliant fuel costs and ethanol's price — particularly low-carbon-intensity supply from the US and Brazil — will determine whether the Tangier Maersk's Houston bunkering becomes a template or a one-off.

By Elena Vasquez