Found this site which i thought might be helpful Click Here .

 

its simple enough to use pen and paper

 

Nice site, I like that you get to know the money that you spend.
But is true what njtls said, all you have to do is reset when you fill up the tank and at the end when you put gas again divide the # of miles by the amount of gallons you put in and thats your mpg. Simple.
PS. I got 27.6 mpg on a long trip doing 80mph and a/c "ON", so I am happy with that.

 

wow....thats some good gas mileage....i seriously think somethings wrong with my car....the best ive ever gotten is 17.1 mpg...and that was me trying to get good gas milage...of course..im mostly local..that still seems low tho

 

i know its easy with pen and paper acutally i use phone and gas receipt when i get home after filling up....just thought it was cool