The density data of Li2O-, Na2O-, CaO- and BaO- Ga2O3- SiO2 glasses have been analyzed. The analysis is based on a structural model predicted from the results of the current spectroscopic investigations. It is assumed that for (R2O or RO)/Ga2O3 = 1 the modifier oxide is used only by the gallate network to form GaO4 tetrahedra without non-bridging oxygen ions. For 1 < (R2O or RO)/Ga2O3 &LE;2 the excess of modifier form non-bridging oxygen ions in the gallate network. There is a remarkable difference between the determined and the calculated density for Ga2O3/SiO2 > 0.75. This is suggestive for a different distribution of the modifier oxide between the two networks. Empirical relations have been obtained to calculate the density as a function of the composition.