Electrical conductivity measurements were performed on Gd2Sn2O7 as a function of temperature, Po-2 and Ca doping concentration. An effective frenkel constant and oxygen vacancy mobility were derived. The high level of intrinsic anion disorder is consistent with expectations based on the cation radius ratio (r(A)/r(B)) in A(2)B(2)O(7) pyrochlore compounds. These measurements were extended to the solid solution Gd-2(Ti1-xSnx)(2)O-7 and Gd-2(Zr1-xSnx)(2)O-7. Intrinsic anion disorder was correlated with x or r(A)/r(B). Systematic decreases in oxygen vacancy mobility with increasing Sn content were observed. An apparent second ionic plateau in sigma plot of sigma vs. Po-2 was found at low Po-2 in Gd-2(Ti1-xSnx)(2)O-7 (x less than or equal to 0.6) which appears to be connected with the reduction of Sn4+ to Sn2+. The variations in ionic carrier density and mobility with composition are discussed in light of appropriate defect models and structural evolution of the lattice.