Abstract: Apparatus for monitoring oxygen saturation levels in tissue for a miniature wireless disposable optical tissue oximeter to are disclosed. According to one aspect of the present invention, a sensor contains a first light source, a second light source, a photodetector, and a skin contact detector. Once skin contact is detected, the first light source emits light in the near infrared region, and the second light source emits light in the visible red region. The emitted light passes through a transparent layer of an adhesive fixation unit, and enters the underlying tissue, where a portion of the light is absorbed by tissue chromophores, including oxygenated hemoglobin and deoxygenated hemoglobin, and reflected back out of the tissue into the photodetector. The oxygen saturation of the tissue under the sensor is then calculated.