The book is divided into eight chapters, where the reader will find works carried out by the Fuel Analysis Laboratory of the State University of Londrina, addressing the analysis of biofuel mixtures from different raw materials; optimization of alcoholic fermentation of extracts obtained from native Brazilian fruits; mathematical modeling in the efficiency of natural and synthetic antioxidants; the influence of metallic contaminants in oxidation; evaluation of catalysts in the biodiesel production and a proposal of mechanisms for the oxidation reaction in the presence of transition metals.