Synergistic effect of the surfactant mixture of ionic liquid 1-dodecyl-3-methylimidazolium bromide (C(12)mimBr) and sodium dodecyl benzene sulfonate (SDBS) on the phase behavior and the solubilization ability of the microemulsion systems was studied with epsilon-beta fishlike phase diagrams. The middle-phase microemulsion appears at the range of the mole ratios of C(12)mimBr to SDBS 0-0.1 and 0.7-1.0. The solubilization ability (SP*) of the mixed surfactant based microemulsion systems increased markedly compared to the pure C(12)mimBr or SDBS-based microemulsion systems. The mixture of C(12)mimBr and SDBS also shows preferable synergism in the solubility of the alcohol and the composition of the interfacial layer. The effects of alcohols, alkanes and NaCl concentrations on the epsilon-beta fishlike phase diagrams of C(12)mimBr/SDBS (molar ratio = 8:2)/alcohol/alkane/brine microemulsion systems were also investigated. (c) 2011 Elsevier B.V. All rights reserved.