Achieving carbon neutrality in the European Union by 2050 requires deep reductions in greenhouse gas emissions in all forms of transport. Powertrain electrification and hybridisation are growing trends for light vehicles. Instead, electrification of maritime and heavy long-distance transport is far more difficult due to their massive energy needs. Battery technology is also problematic for mobile non-road machinery operating for long periods far from the charging infrastructure. However, fuel choices can significantly influence greenhouse gas emissions from internal combustion engines. Therefore, a transition to alternative fuels is one of the strategies under discussion. This study investigated the emission performance of two alternative fuels: biomethane and tall oil-based renewable diesel. In addition to greenhouse gas emissions, the harmful local emissions originating from fuel combustion were investigated. Biomethane was evaluated through a case study of a RoPax vessel operating in the Baltic Sea. In addition, real-driving emissions from a biomethane-powered city bus were measured. The study of renewable diesel´s emissions was carried out with engine experiments on an off-road diesel engine under laboratory conditions. Greenhouse gas emissions were calculated over the entire life cycle of the fuels. The results showed that using renewable fuels derived from sustainable biomass sources can reduce life-cycle greenhouse gas emissions by 65−90 % compared with fossil fuels. In addition, biomethane and renewable diesel can immediately improve local air quality by reducing local emissions. Burning liquefied biomethane reduced particulate matter by 80 % relative to marine diesel oil. Sulphur dioxide emissions were negligible and NOx emissions were low. Renewable diesel slightly reduced all regulated local gaseous emissions. The reduction in particulate number was more significant, at up to 26 % compared with conventional market diesel. Biomethane and renewable diesel proved to be effective ways to decarbonise ...