Three microemulsions containing cosurfactant 2-(2-hexyloxyethoxy)ethanol, 1% aqueous KBr, dodecane, and either didodecyldimethylammonium bromide (DDAB) or cetyltrimethylammonium bromide (CTAB) with conductivities and viscosities appropriate for electrolytic applications were prepared. These fluids were characterized further by measuring diffusion coefficients of electrochemical probes and pyrene fluorescence peak ratios characteristic of polarity and viscosity of the oil phase. A microemulsion of DDAB/2-(2-hexyloxyethoxy) ethanol/1% aq. KBr/dodecane (7.3/36/22.7/34 by weight) had the highest conductivity and lowest viscosity and gave the most positive reduction potential for 4,4’-dichlorobiphenyl of the four-component fluids examined. Electrochemical catalytic reduction of 4,4’-dichlorobiphenyl was done with this fluid, a lead electrode, and zinc phthalocyanine as catalyst with only a small loss of current efficiency compared to a previously used 3-component 21% DDAB microemulsion. The four-component 7.3% DDAB microemulsion was prepared at half the cost of the three-component 21% DDAB microemulsion. On the basis of diffusion, conductivity, and fluorescence studies, the structure of the 7.3% DDAB microemulsion is probably bicontinuous.