▁is ▁a ▁gas oline ▁add itive ▁used ▁as ▁an ▁o xygen ate ▁and ▁to ▁raise ▁the ▁oct ane ▁number . ▁Its ▁use ▁has ▁decl ined ▁in ▁the ▁United ▁States ▁in ▁response ▁to ▁environmental ▁and ▁health ▁concerns . ▁It ▁has ▁poll uted ▁ground water ▁due ▁to ▁M T BE - cont aining ▁gas oline ▁being ▁sp illed ▁or ▁le aked ▁at ▁gas ▁stations . ▁M T BE ▁spread s ▁more ▁easily ▁under ground ▁than ▁other ▁gas oline ▁components ▁due ▁to ▁its ▁higher ▁sol ub ility ▁in ▁water . ▁Cost ▁estimates ▁for ▁removing ▁M T BE ▁from ▁ground water ▁and ▁cont amin ated ▁soil ▁range ▁from ▁$ 1 ▁billion ▁to ▁$ 3 0 ▁billion , ▁ ▁including ▁removing ▁the ▁comp ound ▁from ▁aqu if ers ▁and ▁municipal ▁water ▁supplies , ▁and ▁replacing ▁leak y ▁under ground ▁oil ▁t anks . ▁Who ▁will ▁pay ▁for ▁rem ed iation ▁is ▁controvers ial . ▁In ▁one ▁case , ▁the ▁cost ▁to ▁oil ▁companies ▁to ▁clean ▁up ▁the ▁M T BE ▁in ▁well s ▁belonging ▁to ▁the ▁city ▁of ▁Santa ▁Mon ica , ▁California ▁is ▁estimated ▁to ▁exceed ▁$ 2 0 0 ▁million . ▁ ▁Some ▁U . S . ▁states ▁have ▁en act ed ▁laws ▁to ▁ban ▁M T BE ▁in ▁certain ▁areas . ▁California ▁and ▁New ▁York , ▁which ▁together ▁account ed ▁for ▁ 4 0 % ▁of ▁U . S . ▁M T BE ▁consumption , ▁b anned ▁usage ▁of ▁the ▁chemical ▁in ▁gas oline , ▁effective ▁ 2 0 0 2 ▁and ▁ 2 0