Two-dimensional (2D) phosphorene has been extensively studied for potential electronic and optoelectronic applications. It is easily oxidized by adsorbing oxygen in the air, exhibiting changed materials stability and properties. Yet the impact of oxygen concentrations on stability and electronic properties of oxygen adsorbing phosphorene has never been systematically investigated. In this article, the oxygen adsorbing phosphorene at different oxygen concentrations are studied via first-principles crystal structure searches. We considered stoi-chiometries of P8O, P16O3, P4O and P8O3, with both single-side and dual-side adsorption for selected case P4O. The energetically stable structure of each stoichiometry is identified. It has been found that the band gaps show rather wide range change, strongly depending on the oxygen concentration. Interestingly, at the higher oxygen concentration the relatively low band gaps and small carrier effective masses emerge, comparable with the pristine black phosphorus. This may be associated with the appearance of bridged P-O-P bonds as oxygen concentration increasing. The electronic properties are discussed in relation to structural features and chemical bonding.