This study investigates the usability of the smartphone camera for the evaluation of arterial blood oxygenation (SpO ₂ %). The advantage of this solution derives from the pervasiveness of the smartphone that makes available the evaluation of the SpO ₂ % everywhere. Differently from the pulse oximeter, which uses well-defined wavelength light, the smartphone uses Light Emitting Diodes as a light source to evaluate the SpO ₂ %. The change of the light intensity in the Red and Green colour channels in the video frames of the patient fingertip are properly processed. Two PPG signals are obtained at the wavelengths 600nm and 940nm, respectively. These two PPGs are used to evaluate the SpO ₂ % without calibration coefficients and independently of the smartphone hardware and skin characteristics. Experimental tests are performed to compare the proposed procedure with respect to a commercial pulse oximeter and gas chromatograph. The experimental tests assess the effectiveness of the proposal.