A physiological monitoring system may use photoacoustic sensing to determine one or more physiological parameters of a subject. A photoacoustic signal generated in response to a photonic signal may include multiple peaks as a result of multiple blood vessels and other structures below the surface of the skin of a subject. A photoacoustic system may identify a first and second peak in the photoacoustic signal and determine values from the peaks indicative of physiological parameters. Physiological parameters, such as venous oxygen saturation and arterial oxygen saturation, may be determined based on the values.
