Compressed　air　energy　storage　(CAES)　is　considered　a　promising　energy　storage　technology　because　it　promotes　global　energy　saving,　emission　reduction,　and　the　development　of　renewable　energy.　Improvement　in　the　expander　performance　is　a　major　concern　in　CAES　systems.　The　addition　of　lubricant　is　beneficial　for　reducing　leakage　and　friction　losses,　which　can　improve　the　expander　performance　and　the　CAES　system　efficiency.　To　clarify　the　influence　of　lubricant　on　the　expander　performance,　a　comparative　experimental　study　was　conducted.　A　single-screw　expander　(SSE)　with　different　internal　volume　ratios　and　clearances　was　analyzed　under　different　operating　conditions　with　six　different　lubricant　viscosities　(viscosity　from　small　to　large:　10#,　22#,　32#,　46#,　68#,　and　80#).　The　results　show　that　increasing　the　kinematic　viscosity　of　lubricant　can　effectively　improve　the　volumetric　efficiency.　The　volumetric　efficiency　of　an　SSE　with　a　small　clearance　and　a　small　internal　volume　ratio　is　higher,　and　it　can　approach　100%　with　68#　and　80#　lubricants　when　the　intake　pressure　is　0.5　MPa.　Increasing　the　kinematic　viscosity　of　the　lubricant　reduces　the　shaft　power.　The　shaft　power　of　an　SSE　with　a　large　clearance　and　a　small　internal　volume　ratio　is　larger,　and　the　maximum　shaft　power　with　10#　lubricant　is　5.78　kW　at　0.9　MPa　and　3000　rpm.　The　kinematic　viscosity　of　the　lubricant　significantly　influences　the　shaft　power　of　the　SSE　under　high-speed　conditions,　and　with　the　maximum　variation　being　11.9%.　The　shaft　efficiency　of　an　SSE　with　a　small　clearance　and　a　small　internal　volume　ratio　is　higher,　and　the　gas　consumption　rate　is　lower.　A　low-viscosity　lubricant　should　be　used　to　avoid　over-expansion　when　the　intake　pressure　is　lower　than　0.6　MPa.　The　SSE　with　46#　lubricant　has　good　comprehensive　performance,　where　the　maximum　shaft　efficiency　and　the　minimum　gas　consumption　rate　obtained　experimentally　are　49.29%　and　61.23　kg/(kW.h),　respectively.