Doctoral Thesis / Dissertation from the year 2017 in the subject Environmental Sciences, grade: A, Andhra University (College of engineering), language: English, abstract: Biodiesel as an alternative fuel for diesel engines is becoming increasingly important due to diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum-fueled engines. Biodiesel, which is made from renewable sources, consists of the simple alkyl esters of fatty acids. As a future prospective fuel, biodiesel has to compete economically with petroleum diesel fuels. A two-step transesterification process (Sequential esterification and transesterification process) was used to prepare methyl ester (biodiesel) from high free fatty acid (FFA) content oils. For the yield of high FFA, two-step acid-base catalyzed method has been developed which consists of acid-catalyzed pretreatment/esterification step to reduce the FFA to less than 1% using H2SO4 as an acid catalyst and transesterification of pretreated oil to biodiesel using alkali catalyst. In the present study, the main focus is being placed to explore the non-edible oil resources like Used Cooking Oil (UCO), Cottonseed oil, Jatropha (Jatropha curcas) oil, Neem(Azadirachta indica) oil as a potential source for biodiesel. Experimental results from enzyme (lipase) catalyzed method for selected oils using influencing parameters such as reaction time and catalyst weight, experimental results from acid-alkaline catalyzed methods using common influencing parameters such as methanol to oil molar ratio, catalyst weight, reaction temperature and reaction time for above-mentioned oils were compared using batch mode. Methyl ester (biodiesel) yield range of 66.20-71.6% was attained for an enzyme-catalyzed method, whereas for acid-alkaline the yield range was 84.4-91.6%. This gives the indication of further refinement in the enzyme-catalyzed transesterification process. However, enzyme-catalyzed biodiesel production has some limitations especially when implemented in industrial scale because of the high cost of enzyme, low reaction rate and enzyme deactivation. As the catalyst, an enzyme is restricted to rigorous reaction condition and the activity loss of lipase. The influencing parameters and absolute results of the analysis give the impression of the superiority of acid-alkaline transesterification method for methyl ester production. In this study, we have selected Used Cooking Oil Methyl Ester (UCOME) and Jatropha Methyl Ester (JME) among the methyl esters of four oils.