Darin Lee, who is a well known economic expert regarding airline issues has a fuel calculator on his website. It calculates the portion of any ticket that is due to fuel. It's fun to play with.

According to this article, the average price of jet fuel is $2.56 per gallon, as of October 10, so that means just over 1/4 of my fare from ORD to LGA is due to fuel.

Charlie