Materials that show fast oxide ion conduction have potential applications as electrolytes in devices such as solid oxide fuel cells (SOFCs), gas sensors and gas separation membranes. While bismuth oxide shows the highest oxide ion conductivity of any material, it can only be stabilised at lower temperatures through partial substitution of bismuth by other cations. A total scattering study of the W and La substituted bismuth oxide Bi7W0.25La0.75O12.375 is proposed, with a view to examining details of local coordination and vacancy ordering and their variation as a function of temperature. This compound shows exceptionally high oxide ion conductivity, close to that of pure delta-Bi2O3.The results from the proposed study will be used to shed light on the conduction mechanism in this system.