We will investigate the structural origin of the high sulphate solubility of Ba-rich silicate glasses with radioactive waste immobilisation applications by measuring total scattering data for 8 glasses. Undoped and sulphate-doped (5 mol% SO3) compositions are: 50SiO2-50RxO (R=Li, Na, Ba; 6 samples) and 50SiO2¿25Na2O¿25BaO (2 samples). The results, used in combination with X-ray diffraction data (ISIS Ag-tube diffractometer requested; Diamond proposal submitted), will be used to improve understanding of the effects of composition on the environment of S and, crucially, the effect of S incorporation on the local environments of Si, Li, Na and Ba. This will allow (a) enhanced understanding of the medium-range order of sulphate groups in oxide glasses; and (b) extension of models for sulphur capacities of oxide glasses, with a range of applications including radioactive waste immobilisation.