The paper address a recent changes in political relations between net fossil oil producing countries and net fossil oil consuming countries, instability in oil producing regions as well as the depletion of many existing oil fields make fuel supply is anything but insecure. Development of vegetable oil fuels could lead to greatly reduced dependence on fossil oils. Keeping this in mind possibility of the use of vegetable oils in a diesel engine is experimentally evaluated in the present research. A series of tests are conducted and repeated for each of the test fuels. The engine works at a constant speed of 1500 rpm, but at different loads & blends of used cooking oil. The performance and the behavior of the fuel in diesel engine are analyzed and compared. As vegetable are costly & require large land area for production the used oil of food industry is the best alternative to be used as biofuel regarding cost.