We report on a novel method for sensing oxygen that is based on the use of a perylene diimide dye (1) which is electrochemically reduced to its nonfluorescent dianion form (1(2-)). In the presence of oxygen, the dianion is oxidized to its initial form via an electron-transfer reaction with oxygen upon which fluorescence is recovered. As a result, the fluorescence intensity of the dianion solution increases upon the addition of oxygen gas. Results demonstrate that high sensitivity is obtained, and the emission intensity shows a linear correlation with oxygen content (0.0-4.0% v/v) at ambient barometric pressure. In addition, using electrochemical reduction, oxygen determination becomes regenerative, and no significant degradation is observed over several turnovers. The limit of detection is 0.4% oxygen in argon gas.