The mass culture of microalgae for low cost lipids production requires a detailed understanding of both the physiology of lipid biosynthesis by the selected algal strains and of the factors making these strains competitive in outdoor ponds. Mass culture systems will, because of climatic variability, the day-night cycle, and inherent design factors, exhibit fluctuations in key parameters affecting algal growth, productivity and competitiveness: temperature, pH, po2, pC02, light, and nutrient availability. This project has for its overall objective to quantitate the effects of such fluctuations on culture productivity and species competitiveness. A second objective has been the development of basic information on algal physiology as it relates to lipid productivity.