In this study, the operation of a single cylinder, four stroke, SI engine powered by fuels created by blending two different bioethanol with gasoline was evaluated on the basis of energy and exergy analyses. Within the scope of the study, test engine was tested by operating it with fuel blends, prepared by adding both bioethanol, one of them was produced from waste bread and the other, originating from sugar beet, was supplied, to gasoline at different rates by of 5, 10, 15, 85 and 100% under five different engine loads at maximum torque speed, 2500 rpm. The variation of energy and exergy parameters was examined by comparing the blends, prepared to have similar volumetric content, each other and by comparing all with gasoline. As a result of the study, it was determined that the addition of bioethanol had generally decreasing effect on energy loss rate, exergy loss rate and exergy destruction rate. For fuel blends containing low levels of bioethanol, variation of ethanol has created little differences on all energy and exergy parameters but bioethanol type clearly showed its effect when bioethanol rate increased to 85% and 100%. Although waste bread bioethanol could not catch sugar beet bioethanol in terms of thermal efficiency (14.4% for E100b and 16.4% for E100 as load average) and exergetic efficiency (12.9% for E100b and 14.7% for E100 as load average), both bioethanol have been found to improve both thermal efficiency (12.2% for E0) and exergetic efficiency (11.4% for E0) than that of gasoline.