The thermal expansion of CaTi _0.9M _0.1O _3-δ (M = Fe, Cu, Al) samples has been measured, and their lattice parameters have been refined in space group Pnma. The three materials are shown to be mixed conductors, p-type at high oxygen partial pressures and n-type at low oxygen pressures. At intermediate oxygen partial pressures, the conductivity varies little. The acceptor dopants studied are shown to raise the conductivity of calcium titanate in the order Al < Cu < Fe.