In this article, the transesterification of three types of waste cooking oil (WCO) with methanol and ethanol was studied using alkali catalyzed process. The catalyst used in this study was sodium hydroxide. The effects of temperature, catalyst amount, alcohol to oil ratio, and the time of reaction on the yield were studied. The temperature and the catalyst amount were the most important factors affecting the yield of biodiesel. Also the process exhibited some sensitivity to the level of free fatty acids (FFA) in the WCO and to the type of alcohol. The yields of methyl esters varied from 97% with the lowest acidity (0.4% FFA WCO) to 76% with the highest acidity (3.25% FFA WCO). The ethyl esters yields were lower and the difference increased with the level of FFA in the oil, the maximum yield was 95% and 73% with the lowest and the medium acidities respectively and no reaction was registered with the highest one. The chromatographic analysis of the produced biodiesel showed high contents of fatty acid methyl esters varying from 96.5% to 98%. The physical-chemical characteristics of produced biodiesel were studied and compared to the European norm, EN 14214.