ABSTRACTThe International Maritime Organization is making multiple efforts to reduce greenhouse gas and air pollutant emissions. However, it is difficult to achieve this because of the absence of technological developments. Consequently, there is an urgent need to develop alternative fuels. In this study, marine gas oil and biodiesel were blended at ratios of 0%, 5%, 10%, and 20% to assess their applicability to ships (Component analysis, metal corrosion, and storage stability) and potential for emission reduction (engine performance, environmental effects, and engine durability). The composition of the test fuels meet the ISO 8217:2017 standard. Metal corrosion was insignificant for carbon steel, iron, aluminum, and nickel, but not copper. Storage stability showed no sludge generation or fuel separation, although biodiesel experienced some discoloration owing to its high oxygen content. Engine performance showed no significant differences between marine gas oil and biodiesel. Emissions of NOx increased with higher biodiesel blending ratios, whereas SOx, CO, CO2, and Total hydro carbons decreased. Engine durability was good throughout the 160 hours sea trial. This study demonstrated that even at a 20% biodiesel blending ratio exceeding the 7% ratio suggested by ISO 8217:2017, can be safely used as a long-term marine fuel.