The DiPerna Sweeper, a partial-vacuum oil skimmer, was tested in a two-week test program conducted at the U.S. Environmental Test Tank (OHMSETT) in Leonardo, New Jersey. Forty-three oil recovery tests were run. The object of the program was to establish a range of best performance for the skimmer under various environmental conditions in light and heavy oils. The DiPerna Sweeper is a self-contained, floating oil skimmer that can operate in either a stationary or advancing mode. Its principle of operation is based upon drawing oil and water into a sealed container by creating a slight vacuum in the container. A floating weir serves as the inlet. The partial vacuum is created by pumping fluid from the sealed container. The container serves as an oil/water separator. Separate pumps draw water from the bottom of the vessel while others draw oil from the top. The device was able to recover over 75% of the oil presented to it in calm water at tow speed up to two knots. Performance decreased in waves. Modifications are suggested to improve such performance. The separator functioned well. In one case, the oil offloaded from the skimmer was 95% free of water.