A simple and rapid method for the identification of weathered petroleum oils (passive tagging) by fluorescence spectroscopy is described. The approach used takes advantage of the three-dimensional character of the oil fluorescence spectra. Oil identification methods of other investigators that use fluorescence spectroscopy are also reviewed within the context of the three-dimensional system. Our method involves excitation of the oils at 15 wavelengths, between 220–500 nanometers (nm), at 20-nm intervals. The emission monochromator is rapidly scanned at each excitation wavelength to obtain an emission spectrum. The maximum emission intensities are then plotted versus the excitation wavelengths to derive silhouette profiles. These are used as fingerprints for passive tagging petroleum oils. The influence of weathering, quenching, and solvent effects on our method are also examined.