gas station roulette

I pass a gas station on the way to work every day. This morning at 7:30 the price was $3.24 an hour later at 8:30 the price was $3.19 and when I left work the price was $3.49! What the heck! How can it change so fast? The way I figure it. The gas in the underground tanks didn't change price since it didn't go anywhere. What a crazy world, the bicycle is looking better and better.