Vehicle emissions and performance fueled with waste cooking oil biodiesel is the main topic of this research. Biodiesel was produced through transesterification with physical and chemical characteristics comparable to diesel. B20 is a methyl ester of 20% blended with diesel. A diesel vehicle was modified and equipped with all measuring instruments needed to perform all experiments. The variable speed and load tests were conducted on the vehicle to measure the performance and emissions at different loads (0–30 kW) and different speeds (0–33 km/h). The vehicle speed was the maximum attained for each gear with a constant fuel flow rate without external fuel control at a steady state. At a vehicle speed of 33 km/h, the greatest increases in fuel consumption and exhaust gas temperature for biodiesel B20 were 17 and 6%, respectively, as related to pure diesel. At a vehicle speed of 33 km/h, B20 reduced the distance traveled, carbon monoxide and hydrocarbon concentrations compared to diesel by 22, 9 and 10%, respectively. At a vehicle speed of 33 km/h, the increases in nitrogen oxides and oxygen concentrations of B20 were 4 and 3% higher, respectively, than crude diesel over the whole tested load range. The biggest increases in distance, fuel consumption, and exhaust gas temperature for B20 over diesel were 13, 3, and 2%, respectively, at a vehicle load of 30 kW. The B20 blend decreased CO and hydrocarbon emissions related to diesel by 17 and 32%, respectively, at a vehicle load of 30 kW. The increases in nitrogen oxides and oxygen concentrations of B20 across the whole load range were 11 and 3% higher than pure diesel at a vehicle load of 30 kW, respectively. Biodiesel blend B20 is suggested for application in vehicles providing that the vehicle is moderately loaded.