Abstract: Method and apparatus for precise oil correlation using oil-filled fluid inclusions to form signature plots of fluorescence excitation versus emission versus intensity data. The apparatus uses a tunable light source energized periodically through a given series of wavelengths as directed through a microscope to a fluid inclusion to excite fluorescence. Subsequent fluorescence emission is detected by a monochromator/photomultiplier combination for input to a data acquisition system that processes the data and provides requisite fluorescence output plots indicating more particularly the nature of the fluid inclusion matter, i.e., 3-D fluorescence spectra indicative of the oil. The quality of the oil in terms of API.degree. gravity can also be determined by time-resolution fluorescence spectroscopy to determine fluorescence lifetimes.