Different in situ spectroscopic techniques, including infrared, ultraviolet, and fluorescence, were developed to measure the solubility of organic solids in supercritical carbon dioxide (scCO2). These techniques are applicable over a wide range of concentrations, as low as 10−6 or 10−7 mol fraction, where the conventional flow method is ineffective and less accurate. No separate calibration is required; in fact, the molar absorptivity is determined at the saturation point as an additional benefit. While this technique requires more time per data point, it is more accurate and unbiased than traditional methods at lower concentrations. The Patel-Teja equation of state was used to correlate the data and expand the data for the ternary system. Data are reported for anthracene, 1,4-naphthoquinone, and 2-naphthol in scCO2 and CO2 with methanol cosolvent at 313 K and a pressure range from 7 to 21 MPa.