We studied the effect of reactor filling time (T) (3-5 h), initial mass of inoculum (M) (1000-2100 g), and exponential time decay constant for the substrate feed rate (K) (0.6-1.6 h(-1)) on ethanol production by Saccharomyces cerevisiae grown in sugarcane blackstrap molasses through a fed-batch culture. The highest ethanol productivity (16.9 g/[L (.) h]) occurred at T = 3 h, K = 1.6 h(-1), and M = 1300 g. In addition, productivity was affected by both M (for T = 3 and 4 h) and K (for T = 3 h) and varied inversely with T under any value fixed for M and K. By the quadratic regression multivariable analysis method, equations were determined to estimate ethanol yield and productivity as function of the variables studied (T, K, and M).