I can't say I know what affects gas prices, but I guess it boils down to supply and demand. Getting oil out of the ground is fairly easy, refining it and producing gasoline is the hard (i.e. expensive) part. Refineries in the US have been closing over the years, so instead of importing crude and refining it ourselves, we import refined gasoline which naturally costs more than the homemade stuff. You look at European countries that have no oil production whatsoever and their gas costs more than $5 a gallon, while over here we produce less than half our own gas so the price stays below $3.
Personally I think people should convert their cars to natural gas. It comes out of the ground ready to use so it's way cheaper and it burns cleaner too. But then I also think cars should use gas turbine engines instead of internal combustion, so maybe I'm just crazy.
