Experimental studies have been carried out to investigate effects of biodiesel fuels on diesel engine performance, Carbon monoxide (CO) and nitric oxide (NOX) emissions, exhaust gas temperature (T-Exhaust), oil temperature (T-Oil), wall temperature (T-Wall), and cylinder pressure with/without exhaust gas recirculation (EGR). Biodiesel fuels are prepared from cotton seed oil, palm oil and flax oil. All the measured parameters for biodiesel fuels are compared with the base diesel fuel with/without EGR for different engine speeds. Fuel inlet temperature of 120 degrees C gives minimum viscosity different between diesel and biodiesel fuels. Biodiesel fuels give slightly less brake power (BP), brake thermal efficiency (eta(Bth)) and slightly high brake specific fuel consumption (BSFC) and high fuel mass flow rate per cycle. Diesel fuel gives CO higher than biodiesel fuels due to less O atoms in fuel molecules. Biodiesel fuels give NOX higher than diesel fuel due to high oxygen content in biodiesel fuels molecules and cetane number (CN). As EGR increases, CO increases while NOX decreases due to decrease flame temperature and O-2 in fresh air charge. For biodiesel fuels, T-Exhaust and T-Oil are higher than for diesel fuel. T-Wall for diesel fuel is higher than for all biodiesel fuels. Biodiesel fuels give peak cylinder pressure higher than diesel fuel. The position of peak cylinder pressure is arrangement as 11 crank angle degree (CAD) after top dead center (ATDC) for flax, 12 CAD ATDC for cotton, 14 CAD ATDC for palm and 20 CAD ATDC for diesel fuel respectively. The present work contributes in using biodiesel fuels as alternative fuel for diesel engines without major change for engines parts. For comparison between biodiesel and diesel fuels, the viscosity is not the main parameter affecting on engine performance and emissions. (C) 2013 Elsevier Ltd. All rights reserved.