Electricity　trade　among　power　grids　leads　to　difficulties　in　measuring　greenhouse　gas　(GHG)　emission　factors　of　purchased　electricity.　Traditional　methods　assume　either　electricity　purchased　from　a　grid　is　entirely　produced　locally　(Boundary　I)　or　imported　electricity　is　entirely　produced　by　the　exporting　grid　(Boundary　II)　(in　fact　a　blend　of　electricity　produced　by　many　grids).　Both　methods　ignore　the　fact　that　electricity　can　be　indirectly　traded　between　grids.　Failing　to　capture　such　indirect　electricity　trade　can　underestimate　or　overestimate　GHG　emissions　of　purchased　electricity　in　interconnected　grid　networks,　potentially　leading　to　incorrectly　accounting　for　the　effects　of　emission　reduction　policies　involving　purchased　electricity.　We　propose　a　＂Boundary　III＂　framework　to　account　for　emissions　both　directly　and　indirectly　caused　by　purchased　electricity　in　interconnected　gird　networks.　We　use　three　case　studies　on　a　national　grid　network,　an　Eurasian　Continent　grid　network,　and　North　Europe　grid　network　to　demonstrate　the　proposed　Boundary　III　emission　factors.　We　found　that　the　difference　on　GHG　emissions　of　purchased　electricity　estimated　using　different　emission　factors　can　be　considerably　large.　We　suggest　to　standardize　the　choice　of　different　emission　factors　based　on　how　interconnected　the　local　grid　is　with　other　grids.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.