The extents of the cubic fluorite and pyrochlore regions in the ternary oxide system ZrO2-Gd2O3-TiO2 have been determined experimentally. AC impedance measurements of single phase fluorite and pyrochlore compositions show high oxide ion conduction in compositions containing 20 mol% TiO2. Resolution of the bulk and grain boundary contributions to the total conductivity show that the bulk ionic conductivity increases with Gd2O3 content up to the stoichiometric composition containing 33.33 mol% Gd2O3 and then decreases upon further addition of the aliovalent dopant. Trends in conductivity as a function of temperature and dopant density are discussed.