Lubricating　oil　is　often　employed　in　a　twin-screw　refrigeration　compressor　for　lubricating　bearings,　sealing　leakage　paths,　cooling　refrigerant　gas　and　regulating　capacity.　In　this　paper,　the　effect　of　lubricating　oil　on　the　performance　of　a　semi-hermetic　twin-screw　refrigeration　compressor　is　investigated.　A　mathematical　model　is　established　and　a　comprehensive　experimental　investigation　is　performed　for　this　purpose.　The　model　is　validated　using　experimental　data　and　then　used　to　investigate　the　effect　on　compressor　performance　of　lubricating　oil　supplied　to　the　suction　and　discharge　end　bearings,　and　returned　to　the　suction　pipe.　The　results　show　that　the　compressor　performance　is　reduced　as　the　compensation　oil　injection　flow　rate　increases　in　the　suction　pipe.　However,　as　the　compensation　oil　injection　position　moves　from　the　suction　pipe　to　a　proper　compression　chamber　position,　the　compressor　efficiencies　increase　as　the　oil　flow　rate　increases.　The　results　also　show　that　the　compressor　performance　decreases　as　the　oil　flow　rate　increases　at　the　suction　end　bearing.　But　the　effect　on　the　compressor　performance　of　the　lubricating　oil　supplied　to　the　discharge　end　bearing　depends　on　the　oil　temperature.　Low　temperature　oil　supplied　to　the　discharge　end　bearing　increases　the　compressor　performance,　while　high　temperature　oil　lowers　the　compressor　performance.　These　analyses　provide　useful　information　for　optimizing　lubricating　oil　distribution　to　maximize　energy　efficiency　in　semi-hermetic　twin　screw　refrigeration　compressors.　Crown　Copyright　(C)　2016　Published　by　Elsevier　Ltd.　All　rights　reserved.