The climate neutrality of air and sea transport can hardly be achieved without the accelerated use of almost GHG-neutral fuels. Such fuels are generated from renewable electricity and are thus called electro fuels or (synthetic) e-fuels. To illustrate how these e-fuels can be made available and how to ensure that in both sectors only such fuels are used, several policy roadmaps have been sketched. In terms of e-fuel supply, there are significant differences between aviation and maritime transport: While e-kerosene is widely identified and accepted as future fuel for aviation, a single prospective fuel has not yet emerged for maritime transport. Currently, there is a challenging dilemma for policy makers. On the one hand, the transition towards defossilizing international transport should be accomplished by 2050, requiring that the right decisions are made sooner rather than later. Particularly for shipping, the main goal for the years ahead is, on the other hand, to limit the number of e-fuels pursued. Unless a dominant fuel or fuels are supported by a critical mass of countries, it will hardly be possible to trigger the economies-of-scale dynamics required to accomplish the transition. Our assessment also shows that the first regulatory steps must be taken immediately on all levels.