▁E oc ene ▁se ism ic ▁reflection ▁horizon ▁was ▁mapped , ▁showing ▁a ▁few ▁hundred ▁feet ▁of ▁relief ▁over ▁the ▁entire ▁complex , ▁compared ▁to ▁a ▁ref raction ▁map ▁showing ▁up ▁to ▁ 6 1 0 ▁m . ▁After ▁dr illing ▁the ▁first ▁two ▁well s ▁in ▁C - 6 5 ▁( A ▁and ▁B ▁structures ), ▁an ▁E oc ene ▁map ▁showed ▁the ▁C ▁structure ▁as ▁having ▁ ▁of ▁closure . ▁This ▁was ▁considered ▁sufficient ▁just ification ▁to ▁proceed ▁with ▁dr illing . ▁ ▁Str ucture ▁ ▁The ▁Sir te ▁Bas in ▁province ▁ranks ▁ 1 3 th ▁among ▁the ▁world ’ s ▁pet role um ▁provinces , ▁having ▁known ▁res erves ▁of ▁ ▁of ▁oil ▁equivalent ▁( ▁of ▁oil , ▁ ▁of ▁gas , ▁ ▁of ▁natural ▁gas ▁liqu ids . ▁It ▁includes ▁an ▁area ▁about ▁the ▁size ▁of ▁the ▁Will ist on ▁Bas in ▁of ▁the ▁northern ▁United ▁States ▁and ▁southern ▁Canada ▁( ≈ 4 9 0 , 0 0 0   km ²). ▁Late ▁Mes oz o ic ▁and ▁T ert i ary ▁features ▁developed ▁on ▁a ▁P rec amb rian ▁bas ement ▁and ▁er oded ▁Pale oz o ic ▁surface . ▁The ▁main ▁north west - to - s out heast ▁syn cl inal ▁tr ough ▁experienced ▁repeated ▁subs idence ▁during ▁fault ▁adjust ments . ▁Several ▁regional ▁hor st ▁and ▁gra ben ▁tr ends ▁origin ating ▁in ▁the ▁Late ▁C ret ace ous ▁remained ▁active ▁during ▁the ▁T ert i ary ▁as ▁the ▁Bas in ▁continued ▁subs iding