Another anecdote! Who'd have thunk it!
Here's where gasoline/petroleum prices are set:
http://bloomberg.com/markets/commodities/cfutures.html
With your keen observation that prices always increase before Memorial Day you could make a real killing, just like Hillary turned $1000 into $100,000 in ten months in the cattle futures market.
Your observation that gas consumption was going up over memorial day is a good one. Only two solutions for lower prices 1. lower consumption or 2. more production