- f uel ▁across ▁periods . ▁In ▁particular , ▁if ▁average ▁stage ▁length ▁for ▁the ▁air line ▁has ▁changed ▁significantly , ▁this ▁could ▁have ▁a ▁significant ▁impact ▁on ▁C AS M ▁ex - f uel . ▁ ▁South west ▁Airlines ’ ▁first - qu arter ▁of ▁ 2 0 1 8 ▁C AS M ▁ex cluding ▁fuel ▁and ▁special ▁charges ▁was ▁ 8 . 6 5 ▁c ents , ▁roughly ▁equivalent ▁to ▁Jet Blue ▁Air ways ▁and ▁more ▁than ▁ 2 0 % ▁lower ▁than ▁American ▁Airlines , ▁United ▁Airlines ▁and ▁D elta ▁Air ▁L ines , ▁while ▁U L CC s ▁are ▁lower ▁like ▁Spirit ▁Airlines ▁at ▁ 5 . 8 3 ▁c ents ▁while ▁Front ier ▁Airlines ' ▁is ▁und is closed . ▁ ▁Re venue ▁per ▁AS M ▁( R AS M ) ▁▁ ▁R AS M ▁is ▁a ▁commonly ▁used ▁measure ▁of ▁unit ▁re venue ▁for ▁air lines , ▁expressed ▁in ▁c ents ▁received ▁for ▁each ▁available ▁seat ▁mile ▁and ▁determined ▁by ▁div iding ▁various ▁measures ▁of ▁operating ▁re venue ▁by ▁Av ailable ▁Se at ▁Mil es . ▁ ▁This ▁number ▁is ▁frequently ▁used ▁to ▁allow ▁a ▁comparison ▁between ▁different ▁air lines ▁or ▁a ▁comparison ▁of ▁the ▁same ▁air line ▁across ▁periods . ▁ ▁In ▁theory , ▁the ▁higher ▁the ▁R AS M ▁the ▁more ▁prof itable ▁the ▁air line ▁should ▁be , ▁assuming ▁that ▁the ▁C AS M ▁remains ▁constant . ▁ ▁Vari ous ▁measures ▁of ▁re venue ▁may ▁be ▁used . ▁Pass enger ▁R AS M ▁(