We have thoroughly investigated the effect of oxygen nonstoichiometry on the electrical transport characteristics of ZnO1−δ films. These films were grown on optical grade quartz substrates by using a pulsed laser deposition technique. In order to alter the amount of oxygen nonstoichiometry (δ), oxygen partial pressure during the film growth was systematically varied from 102Torrto10−5Torr. Qualitative estimates about the amount of oxygen nonstoichiometry in these films were made using Raman Spectroscopy data. High resolution electrical resistivity and thermoelectric power measurements were performed in the temperature range 12–300K. A detailed analysis of electrical transport data showed a transition from band-gap insulating state (for the films prepared at high oxygen environments) to Anderson localized insulating state (for the films prepared at lower oxygen environments).