A direct aqueous supercritical fluid extraction system directly interfaced to an infrared spectrometer has enabled the analysis of oil-in-water. The supercritical fluid extraction-infrared method totally eliminates the use of any conventional organic solvents. A rapid and convenient on-line supercritical fluid extraction-infrared calibration method has been developed. With the rapid calibration method, supercritical fluid extraction-infrared method accuracy for determining Brent Delta crude oil in sets of spiked 500 ml water samples was 94-98.9% with relative standard deviation 4.3-4.9%. Thin film infrared and combined gas chromatography-mass spectrometry studies were performed to characterise the components extracted from Brent Delta crude oil using the supercritical fluid extraction-infrared method. Using a general purpose three-wavelength calculation, supercritical fluid extraction- infrared method accuracy for Brent Delta crude oil was 72-82.7% with relative standard deviation 3.3-10.1%, whereas for diesel method accuracy was 81.4-92% with relative standard deviation 0.9-7.8%. The supercritical fluid extraction-infrared method provides the basis for the indefinite use of infrared spectroscopy for a vital environmental measurement. (c) 2007 Elsevier B.V. All rights reserved.