This work investigates the effects of blending waste cooking oil (WCO) biodiesel with gasoline and kerosene on diesel engine performance, combustion characteristics and emissions compared to fossil diesel. The properties of WCO biodiesel derived through transesterification process, are consistent with the standard limits. Kerosene and gasoline additives are added to biodiesel at ratios of 5 and 10% by volume. Tests are carried out on a diesel engine running at 1500 rpm with various loads. The decreases in peak cylinder pressures for kerosene blends are 2 and 1.5% for K5 and K10, respectively but for gasoline blends are 3.5 and 3% for G5 and G10, respectively about diesel oil. The thermal efficiency at full load for diesel fuel had a value of 18.5% and reduced by 9.0, 7.0, 3.5, and 2.0% for G5, G10, K5, and K10, respectively. The CO emissions values were reduced by 24, 31, 35, 40, and 20% for G5, G10, K5, K10, and WCO biodiesel, respectively. HC emissions were declined by 26, 33, 38, 43, and 21% for G5, G10, K5, K10, and WCO biodiesel, respectively. NOx emissions were increased by 31, 25, 13 and 7.5% when using G5, G10, K5, and K10, respectively about diesel oil. The smoke emissions decreases were 30, 34, 41, and 44 % when using G5, G10, K5, and K10, respectively. WCO biodiesel blended with gasoline or kerosene can be considered good alternatives for fuels in diesel engines due to their improvements in performance parameters, combustion characteristics as well as emissions reduction.