The Texaco E and P Technology Div. has developed two fluorescence techniques to enhance the detection of crude oil extracted from formation samples and to improve mud logging as a formation evaluation tool. The quantitative fluorescence technique (QFT) is a portable field method that uses a single excitation wavelength and measures fluorescence at a narrow emission range. When plotted vs. depth, the intensity measurements generate an oil concentration profile of the well. The QFT has successfully located oil-bearing zones that were difficult to identify with conventional mud-logging techniques. The total scanning fluorescence (TSF) technique uses a more sophisticated ultraviolet (UV) spectroscopic instrument and generates a 3D fluorescence spectrum or ''fingerprint.'' This spectrum results from the total fluorescence contribution of the fluorescing species present in the oil. The unique chemical makeups of different crude oils have spectral characteristics that can be used to predict oil composition or type. The TSF method gives more information than conventional fluorescence techniques. This paper discusses the effectiveness of the QFT and the TSF method for identifying crude oil in the presence of fluorescing drilling-mud additives (such as base oils or diesel) and includes a feasibility study that demonstrates the application of these methods in a North Sea well drilled with an oil-based mud. Examples in wells offshore the Mediterranean Sea and Gulf of Mexico are also cited.