Excess oil on the refrigerant side of chillers is a problem that has received a lot of attention in recent years. It is a costly contaminant.
Studies conducted by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) indicate that not only does oil entrained in a chiller's refrigerant significantly degrade performance, but these chillers also use significantly higher amounts of energy. Of course, this leads to higher utility bills.