Abstract: A boom for containing and collecting oil spilt on the surface of a body of water has a number of pivotally linked tanks which form a continuous length. Each tank is supported in a floating condition in the water with most of its volume immersed. Each tank has an open top, walls and a bottom, and the bottom has holes through which water can pass. Oil which is lifted by wave action over the edges of the tanks will drop into the tanks and displace water through the holes in the bottom. This process will continue until all the water has been displaced by oil, whereupon the tanks are full and can be removed for emptying. The invention relies on the fact that water and oil are immiscible and that water is more dense than oil, so that the oil floats on top.