Thermoelectric properties of Re6GaxSeyTe15-y (0 <= x <= 2; 0 <= y <= 7.5) were studied in the temperature range 90-320K. The measurements revealed p-type semi-conductivity in all samples. Relatively high values of the Seebeck coefficients, alpha, were obtained in all samples. The electrical resistivities and room temperature Seebeck coefficients increased as selenium concentrations increased, for each value of x. The room temperature Seebeck coefficients and resistivities decreased as gallium content increased, for each value of y. Low carrier concentrations were found at room temperatures, in agreement with large Seebeck coefficient values. Measurements suggested hopping conduction between 150 K and 280 K for all samples. Temperature dependences of the Seebeck coefficient below 150 K were accounted for by phonon drag effect. The power factors for the samples were calculated. Theoretical discussions of dependences of the measured quantities on temperature and composition are given. Usefulness of these materials as thermoelectrics is also discussed. Published by Elsevier B.V.