As the aviation industry seeks to lessen its environmental effects, sustainable aviation fuels (SAFs) have emerged as a possible alternative to conventional aviation fuels (CAFs). This chapter compares the properties and specifications of SAF and CAF, offering knowledge of their unique features and consequences for engine fuel system performance and sustainability. Key criteria such as sulphur content, density, flashpoint, freezing point, composition, carbon intensity, and emissions profiles are investigated to emphasise the unique characteristics of each fuel type. In addition, the possibility of SAF integration into the CAF is investigated, considering any necessary adjustments or needs. The findings add to a thorough understanding of the technical concerns related to SAF adoption, allowing for better-informed decision-making and promoting the aviation industry’s transition to more sustainable fuel choices.