To support decarbonization, the maritime industry is increasingly assessing low-emissions drop-in fuels, which can be blended with conventional fuels and used in existing engines. These fuels offer a practical option to reduce emissions across the current fleet without requiring major retrofits, infrastructure changes, or early vessel retirement.

However, drop-in fuels alone cannot meet long-term decarbonization goals. To overcome supply limitations and achieve deeper emissions reductions, the sector will likely rely on a combination of drop-in fuels and alternative fuels such as low-emissions methane, methanol, ethanol, and ammonia. These fuels typically require dedicated newbuilds or retrofitted vessels equipped to meet safety and operability requirements. Even on such vessels, low-emissions drop-in fuels can play an important supporting role as decarbonized pilot fuels needed for ignition of alternative low-emissions fuels.

To support the testing and broader uptake of low-emissions drop-in fuels, this paper provides an overview of the processes that may be required for a new drop-in fuel to be evaluated and potentially adopted by the market. While this paper outlines a single, overarching adoption process, real-world pathways often diverge, and not all stakeholders are involved at every stage. The sequence, duration, and level of engagement vary depending on the fuel, vessel, engine configuration, and the operational experience of the parties involved.

Established drop-in fuels for maritime use are fatty acid methyl esters (FAME, also known as biodiesel) and hydrotreated vegetable oils (HVO). Both FAME and HVO are produced from edible vegetable oils like palm, soybean, and rapeseed oil; or from waste fats, oils, and greases (FOGs), which include used cooking oils, animal fats, palm oil mill effluent, and other residual or waste oils. The International Energy Agency (IEA) foresees that production of FAME and HVO may increase to a combined ~68 million tonnes of oil equivalent (MTOE) by 2030, limited by nature conservation and food security concerns. 1, 2

Ultimately, this supply falls significantly short of the anticipated demand across multiple global industries. Shipping alone today consumes 210–230 MTOE,3 far outstripping the projected availability of FAME and HVO and necessitating the development of additional drop-in alternatives. These alternatives include biomass-derived fuels like pyrolysis oil, hydrothermal liquefaction oil, and cashew nutshell liquid (CNSL). These fuels are not currently covered by the International Organization for Standardization (ISO) standard ISO 8217:2024, which applies to conventional fuels, FAME, HVO, and their blends. For the purpose of this report, fuels falling outside the scope of ISO 8217:2024 are categorized as “new fuels.”

The process for adopting new fuels is unclear, fragmented, and time-consuming, involving many parties whose roles are often poorly defined and sometimes driven by diverging priorities. This complexity is compounded by a lack of harmonization across the regulatory bases, which often sit at the intersection of multiple national and international frameworks, with conflicting requirements and occasionally insufficiently specific regulatory language.

Without a clear mapping of the process and practical guidance, stakeholders interested in testing, supplying, or purchasing new drop-in fuels lack a starting point. Those unfamiliar with the landscape struggle to identify the critical steps and risks, and to assess the associated costs and timelines, while new entrants in the value chain frequently underestimate the process’s complexity. Against this backdrop, this project was launched to identify key stakeholders, map the current approval process for new fuels, identify key challenges, and highlight areas for improvement.