The applicability of an X-band (9·4 GHz) real aperture radar (RAR) and an infrared (IR) radiometer to discriminate between crude-oil spills and monomolecular sea slicks is investigated over the same sea area. The results from quasi-simultaneous overflights over a crude-oil spill and three different sea slicks (oleyl alcohol, di-(ethylenglycol)-mono-isostearyletherand methyl oleate)show that the advantage of an imaging radar is its uniequi vocal potential for surveying large sea surfaces and that the advantage of an IR sensor is its ability to determinate quickly the thick centres of crude-oil spills. However, neither the RAR nor the IR radiometer can discriminate between crude-oil spills and sea slicks. Therefore, an airborne coastal patrol with the objective of monitoring oil pollution must comprise a package of additional sensors, e.g. a microwave radiometer and/or a lidar system.