Compressed air, commonly referred to as the fourth utility, can be found in use almost everywhere. New and old facilities grow and often require additional compressed air capacity. Opportunities may arise to meet these compressed air needs using existing or used rotary screw compressors. While purchasing a new compressor has its advantages, do not dismiss the existing equipment as "not worth the time to overhaul." Since most rotary screw compressors use oil to seal the airend (the component containing the compression chambers), very little wear occurs in the compressor itself. This lack of internal wear means that frequently, the compressor can be returned to like-new condition for a fraction of the cost of a new compressor. The following information is offered to help a mechanic or engineer determine if an existing rotary screw compressor is worth the time to overhaul.