Gas Prices

I don't understand this and if anyone does please enlighten me. We bought gas outside of Rochester, MN for $1.67/gallon. Since moving here to Madison I have paid almost $4/gallon. That seems like a HUGE drop in less than 4 months. It bugs me that I don't know why. Now I do know that gas in Minnesota is always cheaper than gas in Wisconsin. I assume that is state taxes.

I also know that gas in Eau Claire was almost the highest in the state. Higher than Madison and about as high as Milwaukee. I assume that was city taxes.

Of course I know that the cost of a barrel of oil fluctuates. I also know that the government holds some oil in reserve. And they can release some and that can affect the cost.

I don't want to sound like a conspiracy theorist but it seems like something else is going on that I do not understand.

My very simple question is why is gas so low now when it was so high just a short while ago? If anyone knows the answer please explain.