To reduce the climate impact of shipping the introduction of alternative fuels is required. There is a range of different marine fuel options but ammonia, a potential zero carbon fuel, has recently received a lot of attention. The purpose of this paper is to assess the prospects for ammonia as a future fuel for the shipping sector in relation to other marine fuels. The assessment is based on a synthesis of knowledge in combination with (i) energy systems modelling including the cost-effectiveness of ammonia as marine fuel in relation to other fuels for reaching global climate targets and (ii) a multi-criteria decision analysis (MCDA) approach ranking marine fuel options while considering estimated fuel performance and the importance of criteria based on maritime stakeholder preferences. In the long-term and to reach global GHG reduction, the energy systems modelling indicate that the use of hydrogen represent a more cost-effective marine fuel option than ammonia. However, in the MCDA covering more aspects we find that ammonia may be almost as interesting for shipping related stakeholders as hydrogen and various biomass-based fuels. Ammonia may to some extent be an interesting future marine fuel option, but many issues remains to be solved before large-scale introduction.