The phase behavior and solubilization of multiphase microemulsions in mixed anionic-calionic surfactant systems were studied for fixed ratios of water to diesel oil and surfactant to alcohol. In the mixed surfactants (sodium oleate + cctyltrimcthylammonium bromide) /diesel oil/ alcohol/water systems, microcmulsion and birefringent phases are formed by adjusting the surfactant ratio e and the cationic weight fraction δ The bicontmuous—→birefringent→o/w microcmulsion transition takes place with dilution for i-pentanol-containing systems. The birefringent region shrinks rapidly with increasing alcohol and/or CTAB weight fractions in total surfactant concentration. The normal solution→w/o microemulsion transition for n-hcxanol systems and only w/o microemulsion for n-octanol systems were observed along the dilution with diesel oil and water. And microemulsion domain enlarges with increasing ε for three alcohol systems. The optimum surfactant concentration γ increases and the corresponding optimum δ decreases with increasing e and the optimum γdecreases with increasing the alcohol chain length from i-pentanol to n-octanol and the optimum δ decreases in the order of i-pentanol > n-octanol > n-hexanol. Conductivity measurements have been performed in the single phase region of the system containing mixed-surfactants and alcohols at 25°C. The conductivity results indicate where a transition takes place and which these different types of phase structure may be in the single-phase of the system containing anionic-cationic mixed-surfactants.