The green alga Botryococcus braunii is widely recognized as a source of non-fossil oil. However, limitations in Botryococcus biomass production hamper its commercial exploitation. This study examines the effects of nutrients (nitrogen and iron) and environmental conditions (temperature, light intensity and photoperiod) on biomass and oil production in two B. braunii Race B strains, Kossou-4 and Overjuyo-3. The highest biomass and oil production were obtained at a nitrogen concentration of 750 mg l−1, iron concentration of 6 mg l−1, at 25°C and at 135 µmol photons m−2 s−1 with a photoperiod of 16 h light:8 h darkness. Culturing the strains in Blue-green (BG11) medium containing optimized nutrients under optimal conditions resulted in an up to ~10.6-fold increase in biomass. In Kossou-4 and Overjuyo-3 strains, biomass increased from 1.647 g 10 l−1 and 3.137 g 10 l−1 respectively in normal BG11 medium to 17.390 g 10 l−1 and 21.721 g 10 l−1 in optimized BG11 media and growth conditions. This was accompanied by ~8–10.5-fold increase in oil production compared with that in normal BG11 medium. Oil (0.324 g 10 l−1 and 0.211 g 10 l−1) was produced in normal BG11 medium in Kossou-4 and Overjuyo-3 strains respectively, compared with 2.642 g 10 l−1 (Kossou-4) and 2.206 g 10 l−1 (Overjuyo-3) in modified BG11 media under optimized conditions. Therefore, optimization of nutrients and environmental conditions can increase biomass and oil production in the two strains of B. braunii.