A new transparent conducting oxide (TCO), which can be expressed asGa3−xIn5+xSn2O16;0.2⩽x⩽1.6,has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs inGa2O3–In2O3–SnO2are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375&OHgr; cm−1was obtained forH2-reducedGa2.4In5.6Sn2O16.This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-dopedIn2O3.©1997 American Institute of Physics.