Slicks are smooth glassy streaks or patches on the ocean. Prominent slicks are confined largely to near-shore areas where organic production is high. Experiments and observations are described which show that slicks are contaminate films of organic oil, probably derived primarily from diatoms which contain droplets of oil in their cells to assist in flotation and/or as an emergency food supply. Slicks are discernible because of their damping effect on small wavelets. The parallel slicks that develop in light to moderate winds result because the contaminate films pile up at the top of convergences in the homogeneous, wind-stirred layer above the thermocline.