Biofuel (e.g. biodiesel) has attracted increasing attention worldwide as blending component or direct replacement for fossil fuel in fuel energized engines. The substitution of petroleum-based diesel with biodiesel has already attained commercial value in many of the developed countries around the world. However, the use of biodiesel has not expanded in developing countries mostly due to the high production cost which is associated with the expensive high-quality virgin oil feedstocks. This research focuses on producing of biodiesel from low cost feedstocks such as used cooking oil (UCO) and animal fat (AF) via alkaline catalyzed transesterification process investigating the effects of process parameters, for example (i) molar ratio of feedstock to methanol (ii) catalyst concentration (iii) reaction temperature and (iv) reaction period on the biodiesel yield. The biodiesel was successfully produced via transesterification process from low cost feedstocks. It was also observed that the process parameters directly influenced the biodiesel yield. The optimum parameters for maximum biodiesel yields were found to be methanol/oil molar ratio of 6:1, catalyst concentration of 1.25 wt% of oil, reaction temperature of 65 degrees C, reaction period of 2 h and stirring speed of 150 rpm. The maximum biodiesel yields at the optimum conditions were 87.4%, 89% and 88.3% for beef fat, chicken fat and UCO, respectively. The results demonstrate high potential of producing economically viable biodiesel from low cost feedstocks with proper optimization of the process parameters. (C) 2010 Elsevier Ltd. All rights reserved.