Positive-displacement　expanders,　which　are　widely　used　in　small-scale　ORCs　(Organic　Rankine　Cycles),　need　reliable　LOS　(Lubricant　Oil　Supply)　to　get　well　lubrication　and　sealing.　In　the　present　paper,　the　characteristics　of　two　traditional　LOS　schemes　are　examined.　Moreover,　a　modified　one　is　proposed.　Analyses　of　those　elements　that　lead　to　work　loss　of　lubricant　oil　supply　have　been　carried　out　for　all　the　three　LOS　schemes.　The　work　loss　of　lubricant　oil　supply,　which　is　caused　by　the　employment　of　lubricant　oil　pumps,　pressure　drop　in　lubricant　oil　separator　and　other　components　contributing　to　work　loss,　is　evaluated　by　a　definition　of　WLLS　(Work　Loss　Factor　of　Lubrication　Oil　Supply).　Based　on　the　thermodynamic　model　of　ORC　established,　the　calculation　methods　of　WLLS　are　presented.　Through　analyses　of　LOS　schemes　and　calculation　of　WLLS　in　two　typical　ORCs,　it　was　found　that　the　traditional　LOS　schemes　either　can　not　work　reliably,　or　might　cause　up　to　11.5%　and　9.5%　power　decrease.　The　values　can　be　reduced　by　half　in　the　proposed　LOS　scheme,　which　can　also　work　reliably.　Accompanied　with　the　advantages,　the　defects　of　the　new　scheme　were　also　investigated.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.