The Yayoi, a new strain of the green colonial microalga Botryococcus braunii, was cultured with aeration of 2% CO2-enriched air. The final algal concentration on the basis of dry weight reached 1.9 g/L after 45 d with the minimum biomass doubling time of 3.5 d. Hydrocarbon content ranged from 30.9-40.5% on dry weight basis and was higher in the early culture stages. Hydrocarbon composition and its variation during the culture were typical of the B race of B. braunii. Relative percentages of lower botryococcenes, such as C-30 or C-32, increased slightly at the middle stages and then declined with increment of C-34 components. A C-34 botryococcene was dominant throughout the culture period.