Formation of solid solutions with the rhombohedrally-distorted perovskite structure has been found in the LaCo1-x-yFexNiyO3 (x=0.1-0.2; y=0.1-0.3) oxide system. Introducing nickel into the perovskite lattice leads to increasing oxygen nonstoichiometry and electrical conductivity and decreasing thermal expansion. The effect of doping by iron has been demonstrated to be the opposite. Averaged thermal expansion coefficients of the ceramics at 300-1100 K are in the range (18.0 - 20.8)X 10(-6) K-1. For the solid solutions with equal concentrations of nickel and iron, oxygen permeation is limited predominantly by the bulk ionic conductivity. Further substitution of cobalt with nickel results in a sharp increase in the permeation flux due to increasing oxygen nonstoichiometry which is accompanied by an occurrence of the surface exchange limitations of the oxygen transport. The activation energy for electrical conductivity of the perovskites has been calculated to be 10.8-18.4 kJ mol(-1).