The thermoelectric transport properties of polycrystalline, Ba_(8)Ga_(16−x)Ge_(30+x) were characterized from 300 to 1000 K. The carrier density was found to vary precisely with the experimental x as expected from simple electron counting. The experimental data are analyzed within the framework of a single parabolic band model, which is found to accurately describe transport for the compositions of interest for thermoelectric application. The lattice thermal conductivity, calculated with a degeneracy adjusted Lorenz number, does not show a trend with composition and a value of ~1 Wm^(−1) K^(−1) is observed at 300 K. A maximum figure of merit zT = 0.86 is obtained at 950 K, and the optimal doping level for thermoelectric application is predicted to be ~2 × 10^(20) cm^(−3), which corresponds to Ba_(8)Ga_(15.75)Ge_(30.25_ by electron counting. An unexpected transition event is observed near 650 K, which results in a significant increase in the heat capacity.