Conductivities of some tetraalkylammonium halides, viz. tetrabutyl ammonium bromide (Bu4NBr), tetrapentylammonium bromide (Pen(4)NBr), tetrahexylammonium bromide (Hex(4)NBr) and tetraheptylammonium bromide (Hep(4)NBr) were measured at 298.15 K in THF+C6H6 mixtures with 10, 20, 30 and 40 mass% of C6H6. A minimum in the conductance values was observed as concentration increases, which dependent both on the salt and the solvent. The observed molar conductivities were explained by the formation of ion-pairs (M+ + X- <-> MX, K-P) and triple-ions (2M(+) + X- <-> M2X+; M+ + 2X(-) <-> MX2-, K-T). A linear relationship between the triple-ion formation constants [log(K-T/K-P)] and the salt concentrations at the minimum conductivity (log C-min) was given for all salts in C6H6 + THF mixtures. The formation of triple-ions might be attributed to the ion sizes in solutions in which coulombic interactions and covalent bonding forces act as the main forces between the ions (R4N+ ... X-). (C) 2009 Published by Elsevier B.V.