Microalgae are a heterogeneous group of organisms consisting of both prokaryotes such as cyanobacteria and eukaryotes such as diatoms (Bacillariophyta), dinoflagelates (Dinophyta), green algae (Chlorophyta), yellow-green algae (Xanthophyta), and red algae (Rhodophyta) (Brennan and Owende, 2010; Hu et al.,

2008) . Similarly, other oleaginous microorganisms are defined as microorganisms with lipid content in excess of 20%. The number of bacteria that produce lipids that could be used for biodiesel production is very small. As a result, bacteria are mainly used for special lipid produc­tion such as Docosahexaenoic acid (DHA). Many yeasts and fungi also produce high quantities of lipid. Yeasts with high lipid content include Candida curvata (58%), Cryptococcus albidus (65%), Lipomyces strakeyi (64%) and Rhodotorula glutinous (72%). Oleaginous fungi include Aspergillus oryzae (57%), Mortierella isabellina (86%), Humi — cola lanuginose (75%) and Mortierella vinacea (66%) (Meng et al., 2009). In terms of microalgae, species are generally unicellular organisms but there are also a number of sim­ple multicellular organisms that occur as colonial or fila­mentous groups of cells. Microalgae are capable of autotrophic, heterotrophic and mixotrophic growth. Microalgae populate a wide variety of ecological niches due to a wide range of tolerance for various growth con­ditions such as availability of nutrients, salinity, pH and temperature (Brennan and Owende, 2010; Gong and Jiang, 2011; Schenk et al., 2008). Currently, microalgae contribute very little biolipid to the overall bioenergy market as full-scale commercialization has yet to be realized. Despite this fact, microalgae remain the feed­stock with the greatest potential for supplying future demand for bioenergy in the form of liquid fuels. The idea of using microalgae as a source of biolipids for bio­fuel is not a new one, however. For example, the Aquatic Species Program was launched in 1978 by what is now known as the National Renewable Energy Laboratory (NREL) with its main focus being, "the production of bio­diesel from high lipid-content algae grown in ponds, uti­lising waste CO2from coal fired power plants" (Sheehan et al., 1998). Over 3000 microalgae strains were initially collected, 300 of which were eventually identified as oil rich. When the program was officially closed in 1998 the conclusions were that no "fundamental engineering and economic issues" were identified that would hamper the feasibility of large-scale microalgae culture. The au­thors noted, however, that total biomass and algal lipids produced were still below "theoretical potential, and the requirements for economic viability" (Sheehan et al., 1998). The economic viability was, of course, based on a time when oil prices in the United States were among their all-time lowest at less than $20 per barrel (adjusted for inflation). Today the average oil price is approxi­mately $100 per barrel and this, along with increased pressure to reduce GHG emissions as well as significant technical advances, has made microalgae-derived bio­fuels even more relevant to meet current bioenergy demands.