As of this month, Hawaii had the most expensive gas, averaging $3.853 a gallon. That's $1.41 more than the state with the cheapest average gas price, Missouri, where it was $2.446. The spread tops the $1.33 gap in November, which had already been above anything we had seen before. In general, there also has been a consistent trend line toward larger gaps.
"When gas prices drop, that's when the gaps widen out," said Patrick DeHaan, a senior petroleum analyst for GasBuddy. "Stations can be more aggressive, choosing to accept less margins by dropping prices." He points out that there is more unification among stations on the way up. "Price wars play out on the way down, and that's when states tend to break apart from each other," he said. Notice the huge recession-driven gas price drop in 2008 caused large gaps among the states.
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Certain states tend to find themselves on one extreme or the other. In the past 10 years, only three states have held the title as the most expensive, with Hawaii winning that 101 of the past 120 months, while the battle for cheapest state has been much more competitive. In most months (66 out of the past 120), South Carolina or Missouri has had the best prices for consumers.