Abstract: Response surface methodology (RSM) using central composite design was applied to obtain the optimal dissolved oxygen (DO) and nitrogen (N) concentrations for biodegrading MTBE (Methyl tert-butyl ether) and BTEX (benzene, ethylbenzene, toluene, p-xylene). Moreover, the effects of DO, N, and their interaction on the degradation process were evaluated. It was found that N, N(2), DO and DO(2) have significant effects on the efficiency of MTBE and BTEX removal. The removal efficiency when using biostimulation with bioaugmentation (BwB) is higher than with other processes, being greater than 82% at concentrations of 12 and 48 mg l(-1) for DO and N, respectively. However, it was also found that the interaction term of DO x N has no significant effect on the degradation processes.