In the early 1970s, different studies related to the potential exploitation of liquid methane as fuel for long range supersonic and hypersonic commercial aircraft were carried out in the US, in order to verify the competitiveness of an alternative vehicle architecture which could compete against the European Concorde. In the end, the studies did not produce a concrete vehicle concept, but the theoretical foundations of the studies are still valid nowadays. On the other hand, the wide interest in hydrogen for aviation produced, more recently, different concepts and studies, also in the field of high-speed aviation, however often highlighting the limitations related to storage capabilities and thermal management.