We report on the electrical properties of a-IGZO thin films prepared by reactive sputtering. Without oxygen injection, dc resistivity measured at room temperature is rho(300K) = 1.22 x 10(-3) Omega m. The lowest resistivity rho(300K) = 4.86 x 10(-5) Omega m is obtained at a certain oxygen supply into the deposition process. Hall effect measurements of these films reveal a metallic-like behavior from mobility and carrier concentration vs. temperature in the range 15-300 K whereas films deposited without oxygen or for the highest oxygen flows behave as semiconductors. These enhanced electrical properties are connected to the oxygen vacancies and the local coordination structure around the In3+ cations. (C) 2014 Elsevier B.V. All rights reserved.