The influence of the media constituents potassium nitrate, magnesium sulphate, dihydrogen potassium phosphate and ferric citrate on growth and hydrocarbon production in Botryococcus braunii (SAG 30.81) was investigated using response surface methodology (RSM). Among the individual variables, potassium nitrate and ferric citrate exhibited marked effects on the response functions (yield of biomass and hydrocarbon production). A high correlation coefficient (r >= 0.93, p <= 0.01) indicated the suitability of second-order polynomials to predict the response function. The optimum concentration of dihydrogen potassium phosphate, potassium nitrate, magnesium sulphate and ferric citrate were 0.16, 0.05, 0.10 and 0.025 g L-1, respectively, in the medium where hydrocarbon production was about 50% on dry weight basis. The optimum concentrations of dihydrogen potassium phosphate, potassium nitrate, magnesium sulphate and ferric citrate were found to be 0.0195, 0.05, 0.02 and 0.0185 g L-1, respectively, in the medium for 0.65 g L-1 biomass and 50.6% (w/w) hydrocarbon production. B. braunii (SAG 30.81) was identified as A race by mass spectra of hydrocarbons it produced. (c) 2005 Elsevier Ltd. All rights reserved.