The early detection of melanoma is critical for patient survival. One of the indentifying features of new malignancy is increased blood flow to the lesion. Multispectral transillumination using the Nevoscope has been demonstrated to be an effective tool for imaging the sub-surface vascular architecture of skin lesions. Using multispectral images obtained from this tool in the visible and near-infrared range, as well as the relative difference in spectral absorption due to oxyhemoglobin and deoxyhemoglobin, we propose an empirical method to estimate the blood flow volume within a skin lesion. From the images, estimates of the distribution of both Hb and HbO2 are calculated along with a ratiometric feature describing the relative oxygen saturation level in the blood. We validate our proposed method through the imaging of a skin phantom with embedded capillaries which can be filled with either an artificial Hb or HbO2 liquid. Our near-IR, multispectral computations nicely differentiate the Hb filled phantom versus the HbO 2 filled phantom, demonstrating that these chromophores can be successfully separated and individually characterized for use in estimating the relative oxygen saturation of skin tissue.