The aim of this study is to select the best blend between alternative blends of fish oil and diesel using multi-criteria decision making technique. The six alternative fuel blends Diesel, B20, B40, B60, B80, and B100 are prepared by varying the amount of diesel in biodiesel. Brake thermal efficiency, exhaust gas temperature, oxides of nitrogen, smoke, hydrocarbon, carbon monoxide and carbon dioxide, are considered as evaluation criteria. A single-cylinder, constant speed and direct injection diesel engine with a rated output of 4.4 kW was used for exploratory analysis of evaluation criteria at different load conditions. The model fuzzy analytic hierarchy process (FAHP), grey relational analysis (GRA) and technique for order preference by similarity to ideal solution (TOPSIS) are proposed to evaluate the best fuel blend. FAHP is used to compute the criteria weights whereas GRA and TOPSIS are combined together and proposed as GRA-TOPSIS for obtaining the final ranking of alternatives. The result of the proposed methodology prioritised the fuel blend as B 20 > B 40 > B 60 > B 80 > B 100 > Diesel. © 2013 Taylor & Francis.