Lubricants are widely used to reduce friction in bearings and other contact surfaces in compressors applied in vapor compression heat pumping, air conditioning and refrigeration systems. The lubricant also serves as a sealant to reduce leakage and helps in reducing the compression discharge temperature by cooling the compression process. Most systems are designed so that the lubricant that enters the compression chamber is discharged and circulates throughout the system. Depending on the system design and flow rates, significant lubricant can be retained in the compressor suction and discharge vapor lines that can lead to reduced efficiency and reliability. Thus, it is important to understand the relationship between oil retention and operating conditions. In this paper, the oil retention in compressor suction and discharge lines is experimentally investigated under various operating conditions with a wide combination of refrigerants (R410A, R32, R1234ze, and R452A) with two different POE (polyolester) oils (POE 32 and POE 100). A test apparatus was designed and constructed to measure the oil retention in both discharge and suction lines with controlled saturation temperature, superheat, refrigerant mass flux, and oil circulation ratio (OCR). The influence of operating conditions as well as the oil type on oil retention is studied to better understand the oil management in vapor compression cycles and provide guidance to system designers.