Solid electrolytes based on Bi2O3 exhibit high conductivity at intermediate temperatures (300-600 deg C) and recent research has revealed the true potential of these materials in intermediate temperature solid oxide fuel cells (IT-SOFCs). There has been much concern about long term stability of bismuth oxide based fluorites, with many systems showing ageing effects that reduce conductivity. Partial double substitution of bismuth by can in some cases lead to greater stability. In the present work we seek to examine possible local cation ordering and its influence on oxide ion distribution and conductivity in the double substituted bismuth oxide fluorite Bi3Y0.5Yb0.5O6 using Reverse Monte Carlo combined analysis of total neutron and X-ray scattering data.