The basic riff for gasoline (this is for beginners) goes like this

E-------------------------------------------------
B-------------------------------------------------
G--------------2h4--4-----------------------------   PLAY 3 TIMES
D-------0h2---------------------------------------
A---2-2-----2-------------------------------------
E-------------------------------------------------

E--------------------------------------------------
B--------------------------------------------------
G--------------------------------------------------    4th TIME
D---2-2----2---------------------------------------
A-------5----5--2-2--------------------------------
E--------------------------------------------------



i know this is real basic but its just to keep the begginners happy and give them something they can play.