As kenshin said, depending on how aggressive you drive, and whether you got the v6 or the i4, Personally I use a 95ron I get about 600-650 a tank on urban roads.
LOLs :P I use prepsol, alternatively you can use this product called oompf from safeway,I heard its a house cleaning thing that gets rid of sticky stuff,
Also: we picked up my cousins brand new lancer yesterday..
*blurred out for privacy purposes mitubishis goin' hunt me down hehehehe xD*
you mad mitsubishi ?