Four green microalgae (TRG, KB, SK, and PSU) identified as Botryococcus spp. by morphological criteria were isolated from lakes and freshwater ponds in southern Thailand. In nitrogen-rich medium the strains achieved a lipid content of 25.8%, 17.8%, 15.8% and 5.7%, respectively. A combination of nitrogen deficiency, moderately high light intensity (82.5 mu E m(-2) s(-1)) and high level of iron (0.74 mM) improved lipid accumulation in TRG, KB, SK, and PSU strains up to 35.9%, 30.2%, 28.4% and 14.7%, respectively. The lipid contents and plant oil-like fatty acid composition of the microalgae suggested their potential as biodiesel feedstock. (C) 2010 Elsevier Ltd. All rights reserved.