Fuels used on green shipping corridors would have to cut carbon intensity by a set margin, measured well-to-wake in CO2-equivalent terms, under a common standard proposed by the International Council on Clean Transportation (ICCT).

The definition would count every tonne of greenhouse gas from producing a fuel to burning it on board. ICCT wants the accounting done with life-cycle methods borrowed from the California Low Carbon Fuel Standard, the state programme that obliges suppliers to cut the average carbon intensity of transport fuels sold in California.

Fuels that clear the bar would earn an "ultra-low-carbon" label. ICCT calls the threshold ambitious but technically achievable — a signal to corridor participants that compliance is within reach of existing and near-term production pathways rather than a theoretical target.

What does the proposal exclude?

The standard draws hard lines around two widely used claim structures.

First, producers could not claim credit for methane emissions avoided elsewhere. That rule would shut out fuels made from manure or organic waste, which currently qualify on the strength of emissions prevented at a farm rather than emissions saved at the ship. For fuel suppliers selling biomethane into maritime markets, book-and-claim accounting anchored to avoided-emission credits would no longer pass muster on an ICCT-defined corridor.

Second, makers of electricity-based fuels — e-fuels such as synthetic methanol and ammonia — would be barred from drawing grid power in ways that push up emissions in the power sector. The clause closes a gap where hydrogen or ammonia production sited on a carbon-intensive grid could be branded green simply because the final molecule burns clean at the ship.

What earns credit instead?

Wind assistance counts the other way. Because it cuts fuel burn directly rather than offsetting it, ICCT says wind propulsion should earn credit for lowering the greenhouse gas intensity of shipping along a corridor. That gives operators investing in rotor sails, wing rigs or kites a quantifiable role in meeting a corridor's carbon-intensity target, rather than treating efficiency technology as separate from the fuel standard.

The design rewards real reductions at the point of use — on the vessel or in the fuel's production chain — and discounts avoided-emission and grid-shifting claims that have drawn scrutiny in other transport fuel regimes.

Why a common standard matters for corridors

Green shipping corridors are trade routes where alternative fuels, technologies and infrastructure are trialled to demonstrate what they can deliver on emissions. The concept has attracted port authorities, carriers and cargo owners, but each corridor has so far set — or deferred — its own fuel qualification rules.

That fragmentation carries commercial cost. Shippers and carriers signing corridor agreements cannot yet compare fuel claims on a like-for-like basis, and fuel producers face uncertainty over which product specifications will count. A single well-to-wake yardstick would let a carrier contracting e-methanol on one route and biofuel on another measure both against the same carbon-intensity bar.

ICCT has built its proposal around a possible route on the US West Coast, tying the accounting framework to a jurisdiction where life-cycle carbon-intensity regulation already governs transport fuels. If adopted, the standard would give ports, carriers and fuel suppliers on that corridor a template that other routes could replicate.

The proposal remains a think-tank recommendation rather than regulation. But with corridor backers under pressure to show verifiable emissions outcomes, a well-to-wake standard that excludes avoided-methane and grid-shifting credits sets a marker for how stringently future corridor fuel rules are likely to be written.