A　single　screw　expander　(SSE)　is　a　small　to　medium-sized　volumetric　expander　of　high　performance,　which　can　be　used　for　energy　recovery　in　vapor　compression　refrigeration　(VCR)　systems　and　expansion　refrigeration　in　air　compression　refrigeration　(ACR)　systems.　As　an　energy　recovery　device,　expander　operation　improvement　is　helpful　to　improve　the　efficiency　of　the　system.　The　expander,　however,　suffers　from　gas　leakage　losses　and　friction　losses　due　to　the　viscosity　of　lubrication　oil,　where　greater　viscosity　results　in　lesser　gas　leakage　and　more　viscous　friction.　This　study　undertook　an　experiment　to　investigate　six　different　viscosity　lubrication　oils　(oil　viscosity　type　from　small　to　large:　10#,　22#,　32#,　46#,　68#,　and　80#)　under　different　inlet　pressures　(0.5–1.1　MPa)　for　clarifying　the　influence　of　lubrication　oil　viscosity　on　the　operation　of　SSE.　The　results　showed　that　increasing　the　kinematic　viscosity　of　the　lubrication　oil　could　reduce　leakage　loss,　which　results　in　a　maximum　increment　of　volumetric　efficiency　of　23.06%,　and　with　the　use　of　68#　and　80#　lubrication　oils,　volumetric　efficiency　was　the　highest　at　92.7%.　In　contrast,　reducing　the　kinematic　viscosity　of　the　lubrication　oil　could　improve　the　shaft　power.　The　maximum　difference　in　shaft　power　between　10#　and　80#　lubrication　oil　was　greater　than　26%.　The　SSE　had　a　superior　shaft　efficiency　and　a　lower　gas　consumption　rate　by　using　10#　lubrication　oil　at　an　inlet　pressure　＜0.55　MPa,　46#　lubrication　oil　at　an　inlet　pressure　of　0.55–0.9　MPa,　and　80#　lubrication　oil　at　an　inlet　pressure　of　0.9–1.1　MPa.　©　2023