This article presents a comparative energy and exergy analyses of a No.2 diesel fuel, jet fuel and four various biodiesel fuels for four cylinder, four-stroke, direct injection diesel engine. Engine was used to obtain the experimental data at full load conditions between 1200-1600 rpm speed. It was found that the first and second law efficiencies increased with biodiesel addition and the minimum exergy destruction was obtained at the 100 % biodiesel fuels. On the other hand exhaust exergy was found to be inversely proportional to the biodiesel addition. It is also shown with extensive emission analysis that the addition of bio diesel fuels to the standard diesel fuel enhances the emission characteristics of diesel engines