Liquid energy sources, e.g., liquid fuels comprising lipid vesicles having fuel additives such as water are disclosed herein. The liquid energy sources, methods for preparation, and methods of enhancing engine performance disclosed herein employing the lipid vesicles result in enhanced fuel efficiency and/or lowered engine emissions. The invention further relates to liquid energy sources containing such additives which further comprise a polymeric dispersion assistant, which reduces the interfacial tension and coalescence of vesicles during dispersion process and storage, and thereby provide transparent looks to the liquid energy source.