The variation of the molar volume, V, and the glass transition temperature, TQ with the average coordination number, m, for twenty-three glass compositions. belonging to the Ge sSbxSRs_x and Ge70SbxSit0_x families of the Ge-Sb-S system, is reported and discussed. The V-m dependence for the Gel sSbxSgs_x family shows a minimum in V at m=2.4 which is attributed to the floppy-to-rigid transition in network glasses. For both families of the glasses examined, the V-m and T„m dependences show peaks at m=2.52 for GeisSbxSiti_x and at m=2.56 for Ge70SbxSx0_x, corresponding to the respective stoichiometric composition for each family. These features are found to be consistent with topological and chemically ordered covalent network models proposed for the structure of these glasses.