Premium vs regular gas prices
Premium costs 24% more than regular across the United States. What almost nobody publishes is how unevenly that is spread: the same step up the octane ladder costs $1.23 a gallon in Michigan and $0.43 in California.
For most cars, the answer is regular
Octane measures resistance to knock — pre-ignition under compression — and nothing else. A gallon of premium holds no more energy than a gallon of regular, so in an engine that was not built to exploit the higher octane it produces no extra power and no extra miles. If the manual says regular, premium buys nothing you can measure.
Two cases genuinely differ. Where premium is required, the engine runs a compression ratio or boost pressure that needs it, and filling with regular makes the knock sensor retard ignition timing — you lose power and a little economy, and the saving is smaller than the sticker suggests. Where it is recommended, the car is designed to run safely on regular with modestly reduced output. The manual is the only reliable place to find out which of the three you own.
Filling a car that does not require it with premium for a year costs about $469 — 12,000 miles at 25 mpg, at the current national step of $0.98 a gallon. In Michigan the same year costs $592.
The premium step is widest where fuel is cheapest — usually
Premium is a low-volume grade. Its price carries more of the retailer’s margin and less of the wholesale market than regular does, and margins are a state-level business decision rather than a commodity. The result is a step that ranges from $0.43 to $1.23 a gallon — nearly threefold — with no relationship to how far the fuel travelled.
It tends to run the opposite way to the pump price. The cheapest quarter of states averages a $0.86 step; the dearest quarter averages $0.66. So the proportional penalty for buying premium is heaviest in exactly the states where regular is a bargain — Michigan at 29% against California at 8%.
Stated as a tendency deliberately. Across the 51 jurisdictions the correlation between the regular price and the size of the premium step is -0.53 — real, but far from deterministic, and there are states on both sides of it that the rule would get badly wrong. The table below is the whole distribution rather than the headline.
| State | Regular | Midgrade | Premium | Step | % |
|---|---|---|---|---|---|
| Michigan | $4.24 | $4.88 | $5.47 | $1.23 | 29% |
| Wisconsin | $3.91 | $4.48 | $5.10 | $1.19 | 30% |
| Rhode Island | $4.03 | $4.76 | $5.17 | $1.14 | 28% |
| Indiana | $3.55 | $4.13 | $4.66 | $1.11 | 31% |
| Illinois | $4.30 | $4.90 | $5.41 | $1.11 | 26% |
| Ohio | $3.99 | $4.55 | $5.08 | $1.09 | 27% |
| New Hampshire | $4.03 | $4.62 | $5.08 | $1.05 | 26% |
| Maine | $4.08 | $4.64 | $5.12 | $1.04 | 26% |
| District of Columbia | $4.23 | $4.78 | $5.27 | $1.04 | 24% |
| Massachusetts | $4.08 | $4.72 | $5.12 | $1.04 | 25% |
| Vermont | $4.17 | $4.73 | $5.19 | $1.01 | 24% |
| Connecticut | $4.16 | $4.76 | $5.16 | $1.00 | 24% |
| Kentucky | $3.64 | $4.18 | $4.61 | $0.98 | 27% |
| Maryland | $4.09 | $4.71 | $5.03 | $0.94 | 23% |
| New York | $4.19 | $4.74 | $5.13 | $0.93 | 22% |
| Minnesota | $3.89 | $4.33 | $4.81 | $0.92 | 24% |
| Georgia | $3.82 | $4.29 | $4.72 | $0.90 | 23% |
| Alabama | $3.68 | $4.15 | $4.57 | $0.89 | 24% |
| West Virginia | $3.86 | $4.30 | $4.75 | $0.88 | 23% |
| Delaware | $4.08 | $4.65 | $4.96 | $0.88 | 22% |
| Texas | $3.63 | $4.13 | $4.51 | $0.88 | 24% |
| Virginia | $3.88 | $4.37 | $4.75 | $0.88 | 23% |
| New Jersey | $4.07 | $4.67 | $4.95 | $0.88 | 22% |
| Tennessee | $3.62 | $4.08 | $4.49 | $0.87 | 24% |
| North Carolina | $3.73 | $4.20 | $4.60 | $0.86 | 23% |
| Louisiana | $3.63 | $4.09 | $4.49 | $0.86 | 24% |
| South Carolina | $3.62 | $4.08 | $4.48 | $0.86 | 24% |
| Pennsylvania | $4.16 | $4.63 | $5.02 | $0.86 | 21% |
| Arkansas | $3.68 | $4.16 | $4.53 | $0.85 | 23% |
| Mississippi | $3.63 | $4.08 | $4.48 | $0.85 | 23% |
| Iowa | $3.77 | $4.05 | $4.61 | $0.85 | 23% |
| Florida | $3.96 | $4.43 | $4.76 | $0.81 | 20% |
| North Dakota | $3.86 | $4.24 | $4.61 | $0.75 | 19% |
| New Mexico | $3.92 | $4.33 | $4.66 | $0.74 | 19% |
| Colorado | $4.05 | $4.45 | $4.78 | $0.73 | 18% |
| Missouri | $3.73 | $4.11 | $4.45 | $0.72 | 19% |
| Oklahoma | $3.64 | $4.05 | $4.36 | $0.71 | 20% |
| South Dakota | $3.99 | $4.18 | $4.69 | $0.70 | 18% |
| Arizona | $4.38 | $4.76 | $5.08 | $0.70 | 16% |
| Nebraska | $3.89 | $4.11 | $4.58 | $0.70 | 18% |
| Kansas | $3.73 | $4.07 | $4.42 | $0.70 | 19% |
| Montana | $4.26 | $4.58 | $4.92 | $0.67 | 16% |
| Nevada | $4.79 | $5.10 | $5.40 | $0.61 | 13% |
| Wyoming | $4.15 | $4.45 | $4.74 | $0.59 | 14% |
| Idaho | $4.36 | $4.66 | $4.95 | $0.59 | 13% |
| Oregon | $4.68 | $4.94 | $5.23 | $0.55 | 12% |
| Washington | $5.14 | $5.43 | $5.68 | $0.54 | 11% |
| Utah | $4.35 | $4.65 | $4.89 | $0.54 | 12% |
| Hawaii | $5.46 | $5.70 | $5.95 | $0.49 | 9% |
| Alaska | $4.78 | $4.97 | $5.23 | $0.45 | 9% |
| California | $5.62 | $5.87 | $6.05 | $0.43 | 8% |
Frequently asked questions
How much more does premium gas cost than regular?
Nationally, premium averages $5.06 a gallon against $4.08 for regular — a difference of $0.98, or 24%. But the state you fill up in matters more than the national figure suggests: the step is $1.23 in Michigan and only $0.43 in California.
Is premium gas worth it?
For most cars, no. Octane is a measure of resistance to knock, not of energy content — a gallon of premium contains no more energy than a gallon of regular and will not, on its own, produce more power or better mileage. If your owner's manual says regular, premium buys you nothing measurable. If it says premium is *required*, the engine is built for it and running regular makes the knock sensor retard timing, which costs you power and some economy. If it says premium is *recommended*, the car runs safely on regular with slightly less output.
How much does using premium unnecessarily cost per year?
About $469 a year, on 12,000 miles at 25 mpg — that is 480 gallons at the current $0.98 national premium. In Michigan, where the step is widest, the same driving costs $592. For a car that does not require premium, that is the whole of the expense with nothing bought.
What octane is regular, midgrade and premium in the US?
US pumps are labelled with AKI, the average of the research and motor octane numbers, which is why American figures look lower than European RON ratings for the same fuel. Regular is normally 87 AKI, midgrade 89, and premium 91 to 93 depending on the state and the chain. Several high-altitude states — Colorado, Utah, Wyoming, Montana and parts of New Mexico — have historically sold 85 AKI as regular, because thinner air lowers the octane an engine needs.
Why is the premium markup so much bigger in some states?
Premium is a low-volume grade, so its price reflects the retailer's margin more than the wholesale market does, and margins vary by state. There is a moderate tendency for the step to be *wider* where regular is cheap: across the 51 states the correlation between the regular price and the size of the premium step is -0.53, and the cheapest quarter of states averages a $0.86 step against $0.66 in the dearest quarter. It is a tendency and not a rule — plenty of states sit well off it.