Summer gas prices haven’t been this cheap since 2004, and there are growing signs they could slip even lower.<br />Cheap gas is being fueled by sub-$50 oil prices.<br />Another hidden force: a serious oversupply problem.<br />Despite being in the heart of summer driving season, the U.S. is sitting on 241 million barrels of gasoline in storage.<br />That’s the highest level for this time of the year since the government began tracking in 1990.<br />Nationwide, average gas prices dropped to $2.18 a gallon on Friday.
