**5. Conclusion and perspectives**

Microalgae have the potential for the production of profitable biodiesel that can eventually replace petroleum based fuel. Algal-biodiesel production, however, is still too expensive to be commercialized as no algal strains are available possessing all the advantages for achieving high yields of oil via the economical open pond culturing system. Current studies are still limited to the selection of ideal microalgal species, optimization of mass cultivation, biomass harvest and oil extraction processes, which contribute to high costs of biodiesel production from microalgae. Future cost-saving efforts for algal-biofuel production should focus on the production technology of oil-rich algae via enhancing algal biology (in terms of biomass yield and oil content) and culture-system engineering coupled with advanced genetic engineering strategies and utilization of wastes. In addition to oils, microalgae also contain large amounts of proteins, carbohydrates, and other nutrients or bioactive compounds that can be potentially used as feeds, foods and pharmaceuticals. Integrating the production of such co-products with biodiesel is an appealing way to lowering the cost of algal-biofuel production.
