Sparsely distributed ionic surfactants (sodium n-alkyl sulfonates) with varying alkyl chains in a nonionic (C14E5) w/o-microemulsion were studied. A nonmonotonic electrical conductivity as a function of chain length has been observed at the critical percolation temperature of the system. A model is proposed that assumes a mutually affecting chain length dependence of the degree of dissociation of the ionic surfactants and of its solubility in the hydrocarbon medium. The calculated plots are in reasonable agreement with the experimental data.