Conductivity of propylene carbonate-diethyl carbonate ͑PC-DEC͒ and propylene carbonate-ethylene carbonate ͑PC-EC͒ solutions of lithium bis͑oxalato͒borate ͑LiBOB͒ was experimentally determined at temperatures from 60 to Ϫ80°C, salt molalities m from 0.04 to 1.1 mol kg Ϫ1 , and solvent compositions w from 0 to 0.7 weight fraction of DEC and EC. Viscosity of LiBOB in PC-EC was studied through measuring its glass transition temperature T g in the same ranges of m and w. T g was found to rise with m and w of EC, indicating a concurrent change in the of the solution. The of the PC-DEC solution of LiBOB peaked in both m and w thus forming a ''dome'' in its 3D presentation in the coordinates of m and w, while that of the PC-EC solution peaked only in m resulting in an ''arch''-shaped surface. As the was lowered, these surfaces fell in height and shifted in the direction of low . These observations correlated well with the changes of dielectric constant of the solvents and of the solutions with the same set of variables. The measured (T) data for the PC-DEC solution was fitted with the Vogel-Tamman-Fulcher equation for an evaluation of its vanishing mobility temperature and apparent activation energy. The results of and of the LiBOB solutions were further compared with those of LiPF 6 solutions from a previous study. This report parallels two earlier ones 1,2 in both structure and content, those dealing with conductivities and viscosities of propylene carbonate-diethyl carbonate ͑PC-DEC͒ and propylene carobonate-ethylene carbonate ͑PC-EC͒ solutions of LiPF 6 and LiBF 4 , respectively; this report dealing with lithium bis͑oxalato͒bo-rate ͑LiBOB͒.3 As such, this report, while giving full account of the new experimental results, skips over some of the detailed descriptions and explanations that can be found in previous reports. Also, although the measured properties of LiBOB are briefly compared with those of LiPF 6 in this report, a fuller comparison across all three salts and its discussion will be left to another report that is to follow.The aim of this report is mainly to provide a relatively complete picture for the change of conductivity with salt molality m and solvent weight fraction w at different temperatures ͑ symbolizes temperature in degrees centigrade and T in degrees of absolute temperature, K͒ 3 for PC-DEC and PC-EC solutions of LiBOB, denoted here as (LiBOB) m -PC 1Ϫw DEC w and (LiBOB) m -PC 1Ϫw EC w . It is felt that such a picture, together with what is already known of dielectric constant and viscosity of PC-DEC and PC-EC solvents and of and of their electrolytes of LiBF 4 and LiPF 6 , 1,2,4,5 could lead to a clear demonstration of the similarities and differences in the change of with m and w and with for the three important lithium salts in the carbonate solvents and to an elucidation of the mechanisms giving rise to these similarities and differences.As has been amply demonstrated, of an electrolyte of a particular salt is critically dependent on the of the solvent and the of the electrolyte:-rises wi...