Abstract: A collapsible boom for use in confining oil spills on water formed of an elongated curtain of flexible material having along the upper edge a tubular portion and along the lower edge a flexible ballast, such as a chain, the curtain containing a plurality of spaced-apart short length cylindrical floats in the upper tubular edge, each float having a passageway therethrough permitting the flow of air through the float and to all parts of the interior of the upper tubular edge, and at least one closure cap permitting, as the curtain is expanded, air to flow into the upper tubular edge so that the boom when placed on water will float and, when removed from water and collapsed into a stored position will permit air to escape, the opening being closeable while the boom is in use on water.