In this study, fuel quality biodiesels produced from waste frying oil using methanol and ethanol were tested as pure and 20% (v/v) blend with petroleum-based diesel fuel (PBDF) in a direct injection (DI) diesel engine running at 600 Nm and three different engine speeds (1100, 1400 and 1700 rpm). The results showed that the brake specific fuel consumptions (BSFC) of ester fuels were higher than those of petrodiesel. The BSFC of ethyl ester biodiesel was slightly lower as compared with methyl ester biodiesel. The thermal efficiencies of the ester fuels were higher than those of PBDF. Ethyl ester biodiesel had slightly better thermal efficiency than methyl ester biodiesel. In comparison to PBDF, ester fuels emitted less CO and THC emissions but they caused to produce more NOx. CO2 emissions were very close to each other. In general, ethyl ester biodiesel released relatively less emissions than methyl ester biodiesel. (C) 2015 Elsevier Ltd. All rights reserved.