Under ultraviolet radiation all crude oils exhibit fluorescence which varies in intensity and hue. During analysis of fluorescence emission spectra of 105 Colorado, Wyoming, and Alberta, Canada, crude oils, and 10 organic matter extracts, 6 prominent peaks of fluorescence were identified at 4440Aa, 4520Aa, 4720Aa, 4830Aa, 5780Aa, and 6300Aa. Fluorescence of crude oils results from the radiations of many groups of organic compounds, the major ones being the polyaromatic and heterocyclic hydrocarbons. Color of fluorescence is determined primarily by heavy hydrocarbon mixtures whose composition is altered during oil migration. The longer the percolation path and the more active the porous solids encountered along the path, the more complete is the selective removal of fluorescing compounds, shifting fluorescence to shorter wavelengths. Fluorescence color is not affected greatly by source or reservoir environment conditions. Fluoranalysis of 11 crude samples from Lance Creek field, Niobrara County, Wyoming, indicates that Jurassic Basal Sundance crude oils are not indigenous to the Jurassic reservoirs but have migrated from Lower Cretaceous source or reservoir rocks across a thrust fault on the NW. side of the Lance Creek anticline. Fluorescence analysis indicates that the McMurray bitumen from Alberta, Canada, represents an immature crude oil which originated from contiguous Lower Cretaceous source rocks. Flourescence of Cretaceous D and J sandstone crudes from 19 oil fields in the Denver basin, Colorado, indicates that J sand crudes have, in general, migrated farther from source rocks to reservoirs than have D sand crudes from similar sources. Fluoranalyses may be used to determine direction and distance of crude oil migration, to identify source rocks, to assist in the solution of migrational problems complicated by geologic structure, and to determine the states of migration of natural hydrocarbons in oil-field waters.