In his article "Getting Real about the Oxygen Biosignature", Marc Kaufman discusses Dr. Victoria Meadows' most recent paper "Reflections on O2 as a Biosignature in Exoplanetary Atmospheres" published in Astrobiology (doi:10.1089/ast.2016.1578).
Photosynthetic O2 has long been considered particularly robust as a sign of life on a habitable exoplanet, due to the lack of known "false positives"-geological or photochemical processes that could also produce large quantities of stable O2. O2 has other advantages as a biosignature, including its high abundance and uniform distribution throughout the atmospheric column and its distinct, strong absorption in the visible and near-infrared. However, recent modeling work has shown that false positives for abundant oxygen or ozone could be produced by abiotic mechanisms, including photochemistry and atmospheric escape. Environmental factors for abiotic O2 have been identified and will improve our ability to choose optimal targets and measurements to guard against false positives.