This paper investigates diesel engine performance and exhaust emissions with marine gas oil (MGO) and a blend of MGO and synthetic diesel fuel. Ten per cent by volume of Fischer-Tropsch (FT), a synthetic diesel fuel, was added to MGO to investigate its influence on the diesel engine performance and emissions. The blended fuel was termed as FT10 fuel, while the neat (100 vol%) MGO was termed as MGO fuel. The experiments were conducted with a fourstroke, six-cylinder, turbocharged, direct injection, Scania DC 1102 diesel engine. It is interesting to note that all emissions including smoke (filter smoke number), total particulate matter (TPM), carbon monoxide (CO), total unburned hydrocarbon (THC), oxides of nitrogen (NOx) and engine noise were reduced with FT10 fuel compared with the MGO fuel. Diesel fine particle number and mass emissions were measured with an electrical low pressure impactor. Like other exhaust emissions, significant reductions in fine particles and mass emissions were observed with the FT10 fuel. The reduction was due to absence of sulphur and aromatic compounds in the FT fuel. In-cylinder gas pressure and engine thermal efficiency were identical for both FT10 and MGO fuels.