Just drove cross country 3 weeks ago coming back west from the far NE. By far MO. was the lowest with the mid west states overall having lower prices than Can-of-duh, NE US, and western US, both in gas and diesel, although not as much in diesel as regular. This makes no sense to me as my understanding is theses states are further from refineries than the more expensive states.
Fuel taxes can play a big role in the price you pay at the pump.
