An innovative fiber optic setup for the scattering-free absorption spectroscopy of liquids is presented. It makes use of an integrating sphere that contains the sample under test, coupled to a fiber optic supercontinuum source and to a fiber optic spectrometer. The highly-bright broadband light shining on the sphere's surface is diffusely reflected and collected by the fiber-coupled spectrometric detector. When an absorbing medium is placed in the cavity, a reduction occurs in the radiance of the sphere. The reduction is related to the absorption and volume of the medium, and is independent of nonabsorbing objects, such as scattering particles, within it. A collection of turbid lubricant oils was considered as a test case for verifying and validating the innovative scheme of diffuse-light absorption spectroscopy. Scattering-free spectra were successfully measured and processed as product fingerprints for the prediction of turbine types and other parameters that indicate oil quality.