▁Ex - f uel ▁C AS M ▁or ▁C AS M ▁ex - f uel ▁ ▁C AS M ▁ex cluding ▁fuel ▁is ▁a ▁commonly ▁used ▁measure ▁to ▁compare ▁the ▁cost ▁performance ▁of ▁air lines ▁except ing ▁the ▁cost ▁of ▁fuel . ▁Due ▁to ▁the ▁vol at ility ▁of ▁oil ▁prices , ▁air line ▁fuel ▁cost ▁is ▁generally ▁not ▁viewed ▁as ▁cont roll able ▁( other ▁than ▁in ▁the ▁short - term ▁via ▁fuel ▁h ed ging ). ▁Therefore , ▁management ' s ▁success ▁at ▁cont rolling ▁costs ▁is ▁often ▁jud ged ▁by ▁looking ▁at ▁how ▁the ▁air line ' s ▁ex - f uel ▁C AS M ▁changes ▁from ▁one ▁period ▁to ▁another . ▁For ▁instance , ▁in ▁the ▁second ▁quarter ▁of ▁ 2 0 1 1 ▁South west ▁Airlines ▁had ▁fuel ▁costs ▁of ▁$ 1 . 5 2 7 ▁billion ▁( ag ain , ▁including ▁its ▁Air T ran ▁subs idi ary ). ▁South west ' s ▁system ▁C AS M ▁ex - f uel ▁for ▁the ▁second ▁quarter ▁of ▁ 2 0 1 1 ▁was ▁then : ▁ ▁C AS M ▁ex - f uel ▁= ▁( Direct ▁Oper ating ▁Cost ▁- ▁F uel ▁Cost ) ▁/ ▁Av ailable ▁Se at ▁M ile ▁= ▁($ 3 . 9 2 9 ▁billion ▁- ▁$ 1 . 5 2 7 ▁billion ) ▁/ ▁ 3 1 . 4 5 7 ▁billion ▁= ▁ 7 . 6 3 ▁c ents ▁ ▁Again , ▁care ▁must ▁be ▁taken ▁in ▁comparing ▁C AS M ▁ex