A whitepaper published by NorthStandard advises against the use of 100% CNSL as a marine fuel.

Use of cashew nutshell liquid (CNSL) in marine biofuel blends is drawing renewed scrutiny, according to a new white paper from maritime insurer NorthStandard.

The report, developed with bunker supplier World Fuel Services and fuel testing firm VPS, highlights operational risks associated with high concentrations of CNSL in bunker fuels, as per the white paper published on the firm's website on Thursday.

While established biofuel feedstocks such as FAME and HVO are described as having mature specifications and predictable performance, CNSL is not recognised as a standard fuel component under ISO 8217.

The paper states that using 100% CNSL as a marine fuel should be avoided, and also cautions against blending CNSL with HSFO due to potential operational damage

Concerns include high acidity, reactivity and polymerisation risks, which can lead to corrosion, filter clogging, injector fouling and fuel instability if not properly managed.

However, the report notes that improved refining and distillation techniques are helping to reduce some earlier quality issues.

"We know from experience that CNSL-derived products are already in the market, especially in ARA, due to low carbon feedstock demand," Michael Green, Senior Quality Manager- Marine Technical at WFS, said in the white paper. 

The warning comes as marine biofuel use accelerates. VPS tested samples representing 71,000 mt of bunkered biofuel in 2021, rising to more than 1 million mt in 2025, a twelvefold increase.

NorthStandard concludes that as biofuel blends diversify, buyers must apply stronger due diligence and technical controls, particularly when dealing with novel feedstocks such as CNSL.

Another maritime insurance firm Skud had issued a warning against use of CNSL-based biofuels in shipping last year. 

The white paper from NorthStandard can be downloaded from here.