The recast of the Renewable Energy Directive (referred as REDII) was adopted in 2018 [5]: it sets a new overall target for the European Union for renewable energy consumption by 2030 and includes a sub-target for the transport sector. Highlighting that the REDII is already under revision, the expected goal for renewables in the EU transport sector has been set at a minimum of 14% in road and rail transport by 2030. Within this target, a gradually increasing sub-target for alternative fuels produced from advanced feedstocks (the ones listed in REDII Annex IX, Part A: lignocellulosic feedstocks, biomass fraction of mixed municipal waste, etc.) has been planned for the period of 2020-2030: a minimum of 0.2% by 2022, 1% in 2025, and at least 3.5% by 2030. The member states can double-count advanced biofuels, produced from advanced feedstocks, towards both the 3.5% target (thus 1.75% actual volume) and the 14% target. It is worthwhile to stress that the revision of this double-counting mechanism is currently under discussion. Other non-food/feed competing biofuels, which derive from feedstocks that are unsuitable for food or feed applications (the ones listed in REDII Annex IX, Part B--e.g., used cooking oil and animal fat), can also be double-counted towards the 14% target but are capped at 1.7% in 2030. The reason for this cap is linked to the attempt to lower indirect land-use change effects on other sectors, such as food and animal feeding. It is worthwhile to highlight that the REDII targets road transportation only, while no obligations are set for the aviation and maritime sectors. However, for the very first time, the REDII contains a specific multiplier to stimulate the uptake of biofuels in both maritime and aviation sectors. These are the major innovations contained in the REDII that are related to the promotion of alternative fuels for transport. At the European level, the aviation and the maritime sectors have recently been identified as key players for meeting the targets set in the European Green Deal [6]. The European Commission launched the \"fit-for-55\" package [7], which contains two legislative proposals that promote the uptake of alternative fuels; alternative fuels are perceived as a short- or medium-term means to reduce greenhouse gas impacts. If, on one hand, the potential benefits from substituting fossil oil with alternative fuels are evident, then, on the other, the sustainability concerns risk reducing these benefits: the presence and availability of sustainable feedstock is a crucial point. Regarding the use of alternative sustainable fuels in aviation, the United Nation's International Civil Aviation Organization (ICAO) in 2016 adopted a global market-based scheme to limit international aviation CO\({}_{2}\) equivalent (CO\({}_{2e}\)) greenhouse gas emissions (GHG): the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) [8]. CORSIA requires operators to offset their GHG emissions that exceed 2019 levels (estimated by ICAO and ATAG at 915 million tonnes of CO\({}_{2}\)); alternative fuels are one of the main \"intra-sector\" instruments for achieving carbon neutrality [8; 9]. Besides the expected reduction provided by the use of alternative fuels, it is worth remarking that CORSIA is fundamentally an offsetting scheme, allowing operators to use carbon credits from extra-sector initiative, to balance their emissions. At the European level, being part of the fit-for-55 package, the ReFuel EU aviation legislative proposal [10] also aims to contribute to increasing the supply and demand for sustainable aviation fuels. The proposal sets an increasing sustainable aviation fuel (SAF) blending mandate, with a specific sub-mandate for eFuels. Similarly, the Maritime Environment Protection Committee (MEPC) of the International Maritime Organisation (IMO) adopted an initial strategy in 2018 [11] on the reduction of GHG emissions from ships, setting out a vision for 2050.