A fully instrumented catamaran was used to carry out in situ measurements of physical and dynamical properties of slick and clean sea surfaces. The surface tension and wave-damping rate were found to vary across the slick. The latter is further associated with the Marangoni effect. In addition to wave suppression, the augmentation of wind speed and the reduction of wind stress by slicks were recorded. The formation of slick bands was also observed. Finally, surface films influence air-sea transfers and other interfacial processes were discussed. ¿ American Geophysical Union 1992