Although a relatively small contributor to annual anthropogenic CO2 emissions (similar to 2.6%), commercial aviation activity is growing at similar to 5% per annum. As a result, alternative jet fuel (AJF) technologies have garnered interest as a means to achieve large, near-term emissions reductions for the industry. This analysis quantifies the potential for AJF to reduce aviation's CO2 emissions by assessing: the availability of AJF feedstock; AJF volumes that could be produced from that feedstock; the lifecycle emissions of AJF compared to petroleum-derived jet fuel; and the number of bio-refineries and capital investment required to achieve the calculated emission reductions. We find that, if the use of AJF is to reduce aviation's lifecycle GHG emissions by 50% or more by 2050, prices or policies will have to significantly incentivize the production of bioenergy and waste feedstocks, and AJF production will need to be prioritized over other potential uses of these resources. Reductions of 15% by 2050 would require construction of similar to 60 new bio-refineries annually (similar to growth in global biofuel production capacity in the early 2000s), and capital investment of similar to 12 billion USDzois per year (similar to 1/5 of annual capital investment in petroleum refining).