In vapor compression cycles the compressors need oil to prevent surface-to-surface contact, to remove heat, to provide sealing, to keep out contaminants, to prevent corrosion, and to dispose of debris created by wear. A small portion of the compressor oil circulates with the refrigerant through the cycle components, while most of the oil stays in the compressor. The oil amount carried with the refrigerant typically ranges from 0.5 to 1 percent of the refrigerant flow rate circulating in the refrigeration systems. This means that oil might be missing from the compressor because it can accumulate inside the heat exchangers during actual operation of the systems.