This study attempted to investigate variation in biovolume of Scenedesmus obliquus, in the modified Johnson medium at 20 +/- 2 degrees C, under 16 kerg cm(-2) s(-1) continuous illumination. The experiments were carried out at four nitrate (8, 12, 16, and 20 mM) and four phosphate (0.1, 0.3, 0.5 and 0.7 mM) concentrations at pH 7 and 8. The best response for algal growth was found at 0.3 mM phosphate and 12 mM nitrate at pH 7, as it was obtained from weight averaging method. Besides, optimum phosphate and nitrate concentrations significantly distinguished (p < 0.01) from other concentrations according to Tukey's HSD test. Key features of the growth of S. obliquus under phosphate and nitrate influenced batch culture was successfully predicted by modified Gompertz model. Through the cultivations, specific growth rate (p) ranged from 0.30 to 1.02 day(-1), while biovolume doubling time (td) varied from 0.68 to 2.30 days. There were important differences (p < 0.05) for both mu and td among response variables. Both nutrients displayed noteworthy effect (p < 0.01) on the algal biovolume. (C) 2008 Elsevier Ltd. All rights reserved.