In order to maximize microalgae biomass production and reduce its overall costs, it is important to optimize inoculum conditions based on its physical and physiological characteristics. Chlorella sorokiniana cultures inoculated with inoculum at three different physiological stages (lag, exponential, and stationary) diluted to the same optical density were cultivated for 12 days under three different CO2 concentrations (0.038, 5, or 10 % CO2 v/v) and growth pattern and biomass production was observed. Samples inoculated with lag phase inoculum supplied with 5 % CO2 achieved the maximum biomass production, whereas samples supplied with 0.038 % CO2 never reached exponential growth. The better growth of samples inoculated with lag phase inoculum was attributed to its increased number of cells compared to the other two inocula.