ies . ▁Es so ▁d ug ▁three ▁other ▁well s ▁between ▁ 1 9 9 7 ▁and ▁ 1 9 9 8 . ▁El f ▁withdraw ▁from ▁the ▁vent ure ▁in ▁ 1 9 9 8 ▁and ▁Es so ▁was ▁joined ▁by ▁Pet ron as ▁in ▁ 2 0 0 2 . ▁After ▁more ▁than ▁four ▁years ▁of ▁expl oration , ▁Es so ▁and ▁Pet ron as ▁abandoned ▁the ▁Ag adem ▁permit ▁in ▁ 2 0 0 6 , ▁jud ging ▁it ▁econom ically ▁un prof itable . ▁The ▁block ▁thus ▁fell ▁back ▁in ▁the ▁public ▁domain ▁of ▁the ▁State ▁with ▁an ▁estimated ▁ 3 2 4 ▁million ▁bar rel s ▁of ▁oil ▁res erves ▁and ▁nearly ▁ ▁of ▁gas . ▁Unfortunately ▁for ▁the ▁Es so ▁and ▁Pet ron as ▁vent ure , ▁the ▁oil ▁prices ▁sky ro cket ed ▁starting ▁ 2 0 0 7 ▁going ▁from ▁$ 3 0 ▁to ▁$ 1 4 7 ▁in ▁ 2 0 0 8 . ▁The ▁res erves ▁considered ▁me ager ▁became ▁more ▁attract ive ▁and ▁in ▁ 2 0 0 8 , ▁China ▁National ▁Pet role um ▁Corporation ▁through ▁its ▁expl oration ▁and ▁development ▁company ▁( C NO DC ) ▁acquired ▁the ▁permit ▁on ▁the ▁Ag adem ▁block . ▁As ▁part ▁of ▁the ▁agreement ▁with ▁the ▁government ▁of ▁Niger , ▁C NO DC ▁created ▁national ▁branch ▁in ▁Niger ▁( CN PC - N IG ER - P ET RO LE UM ▁SA ) ▁and ▁carried ▁out ▁further ▁expl oration . ▁Between ▁ 2 0