Bio-diesels were produced from transesterification of olive, canola and soybean oils and chicken and caw fat. The resultant mixture of methyl esters was further upgraded via ozonolysis to replace double bonds in unsaturated methyl esters with carbonyl functionalities. Composition and structural information were sought using GC-MS for the bio-diesels produced from transesterification and ozonolysis, in addition to a blend of five Jet-A/A1 fuels. All bio-diesels examined contain methyl C16 and C18 esters mainly, e.g., palmitate, stearate, oleate, and linoleate. The unsaturated species have double bonds mainly at 9 and 12 positions. The hydrogen deficiency of bio-diesels derived from plant oils follows the order of olive oil < canola oil < soybean oil. Class information and structural details, in terms of carbon number and number of substituents, of a JetA/A1 blended fuel were obtained and compared with values reported in the literature. Possible pathways of bio-diesel upgrading are mapped out. Improved fuel properties of upgraded bio-diesels are discussed, including the emission pattern of bio-diesels that is modeled in premixed-flames, which provides insights in the emission reduction of burning bio-fuels.