[jandrese]

Transatlantic shipping also. Planes require highly refined fuel though, while ships can burn most anything flammable, even really crappy biofuels. Hardly anything is worse than heavy fuel oil.

[bryanlarsen]

Different types of density. Transatlantic shipping cares primarily about volumetric density, air travel cares primarily about gravimetric density.

So we can both be correct since OP was not specific. :)