▁level . ▁Trade ▁was ▁based ▁on ▁US ▁doll ar ▁res erves ▁( the ▁only ▁acceptable ▁reserve ▁currency ), ▁which ▁Europe ▁lack ed . ▁ ▁Therefore , ▁the ▁transfer ▁of ▁money ▁( im medi ately ▁after ▁each ▁transaction ) ▁increased ▁the ▁opportunity ▁cost ▁of ▁trad ing . ▁Some ▁trade ▁was ▁reduced ▁to ▁bar ter . ▁The ▁situation ▁led ▁the ▁Organisation ▁for ▁European ▁Econom ic ▁Co - operation ▁( O E EC ) ▁to ▁create ▁the ▁E PU , ▁all ▁members ▁signing ▁the ▁agreement ▁on ▁ 1 ▁July ▁ 1 9 5 0 . ▁The ▁E PU ▁account ed ▁for ▁tr ades ▁but ▁did ▁not ▁transfer ▁money ▁until ▁the ▁end ▁of ▁the ▁month . ▁ ▁It ▁changed ▁the ▁landscape ▁from ▁bil ater al ▁tr ades ▁of ▁necessity ▁( tr ading ▁with ▁partners ▁because ▁of ▁out standing ▁deb ts ) ▁to ▁mult il ater al ▁tr ades . ▁The ▁E PU ▁also ▁forced ▁liberal ization ▁by ▁mand ating ▁that ▁members ▁eliminate ▁disc rimin atory ▁trade ▁measures . ▁The ▁E PU ▁was ▁a ▁general ▁success ▁with ▁trade ▁levels ▁more ▁than ▁dou bling ▁during ▁its ▁existence . ▁By ▁its ▁close ▁in ▁ 1 9 5 8 , ▁convert ibility ▁of ▁currency ▁was ▁a ▁possibility , ▁no ▁longer ▁need ing ▁government ▁permissions ▁in ▁European ▁countries . ▁ ▁See ▁also ▁ ▁Bre tt on ▁Wood s ▁system ▁▁ ▁Marshall ▁Plan ▁Asian ▁Clear ing ▁Union ▁European ▁Pay ments ▁Council ▁European ▁System ▁of ▁Central ▁B anks ▁International ▁Clear ing ▁Union ▁ ▁References ▁▁ ▁Bald win , ▁Richard ▁and ▁Charles ▁Wy pl osz