A real-time, non-invasive method for measuring venous oxygen saturation (SvO2) would offer promising outcomes for ICU care, especially in diagnosing sepsis and optimizing care, for mechanical ventilation and blood transfusions. This research proposes a low-cost (US$170), proof-of-concept, reflectance optical sensor capable of measuring arterial-venous oxygen saturations at the finger. By introducing a digit cuff actuator system, pulsations at low frequency and pressure were induced in the venous system, allowing separate processing of arterial and venous signals. Three different methods were utilized for signal processing in MATLAB: Peak and Trough Detection, Fast Fourier Transforms, and Power Spectral Density. An evaluation trial with five healthy adult subjects demonstrated the sensor's ability to estimate SpaO2 and SpvO2, with results comparable to literature values. While SpaO2 values trended lower than expected, with median SpaO2 ranging from 89.27% to 93.78%, SpvO2 values remain within the normal range of 60-90% with subject trial medians between 76.99% and 84.30%. Small standard deviations between tests and estimation methods confirmed the reliability of the system, with consistent arterial estimations between normal and induced pulsation tests, proving both arterial and venous saturations can be measured and estimated near simultaneously. SpaO2 values are likely lower due to a lack of calibration with a blood gas analyzer and from using an empirically derived model equation determined for a transmittance sensor. However, the sensor with calibration and validation on a large test cohort shows potential for low-cost, non-invasive estimations of both SpaO2 and SpvO2 and thus oxygen extraction monitoring, providing potential for improving patient outcomes while reducing risks and costs.