Sustainable aviation fuels (SAFs) are the near-term technological solution to decarbonize the aviation industry sector. There are several pathways to obtain biojet fuels, which can be classified into four main categories, namely oil-to-jet, alcohol-to-jet, gas-to-jet, and sugar-to-jet. All of them share the need for hydrogen to obtain a drop-in fuel that can be blended with petroleum-based jet fuel. The hydrogen input requirements affect the life cycle greenhouse gas emissions, increase the biojet fuel cost and hinder the construction of distributed processing plants. This study addresses the problem of hydrogen sourcing in the production of SAFs through a systematic literature review. Techno-economic studies of biojet fuel production using different feedstocks and conversion pathways are analyzed focusing on the methods of hydrogen provision. The technological options used to generate the required hydrogen within the conversion process itself as well as externally, along with the main strategies to reduce the hydrogen demand are identified. The production yields and the hydrogen consumption of several SAF production pathways are compared. The jet fuel yields reach values as high as 0.66 for hydroprocessing of vegetable oils with external hydrogen provision, while they drop to 0.10 for production from lignocellulosic biomass with internal hydrogen sourcing. The results of the analysis highlight the real potential of four among the most promising routes for the production of biojet fuels when the burden related to hydrogen demand is properly taken into account
