&gt; This inefficient use of volume is probably a more severe limiting factor than the weight.<p>I don&#x27;t necessarily disagree with you.  However, weight is a really, really big deal in aircraft.  And the volume becomes less of an issue as aircraft get bigger, thanks to the square-cube law.  Are modern day jet aircraft big enough to largely offset the costs of fueling them with liquid hydrogen?  I don&#x27;t know, but they&#x27;re pretty damn big.