This work studied the production of biodiesel from waste cooking oil using an ultrasonic reactor and the testing of biodiesel fuel performance in a diesel engine on a light truck. The process for biodiesel production consisted of several steps, including waste cooking oil filtration, esterification, ultrasonic-assisted transesterification, biodiesel separation using the decantation process, washing, and drying. The main transesterification reaction was conducted using methanol with a molar ratio