This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when used with waste vegetable oil. The method overcomes the inherently slow transesterification reaction by using 1-propanol in place of methanol. The higher reflux temperature of 1-propanol and the improved mixing between the phases when 1-propanol is used allows the reaction to be completed in about one hour. The biodiesel fuel is analyzed by simple flammability and viscosity tests. The exercise, although not practical for large-scale production of biodiesel, serves to illustrate the concept of transesterification. (Contains 3 notes, 1 figure, and 4 schemes.)